AIBU to feel upset after my meeting with my manager?

You shouldn't be carrying that much stress in a minimum wage job.
You shouldn't be downgraded on a basis of your personality when interaction with customers is good and your work is good.
You should leave as soon as you can, the management sounds absolutely horrendous. The way you've stepped up in managing the team when the manager isn't there and have took on extra work sounds like you're worth so much more than what you're getting. Believe in yourself, put yourself out there and apply for higher paying jobs. You are so much more than what this manager sees in you and plenty of employers would appreciate what you can bring to a team.

I would not write any more than "here is my sick note." Let them figure the rest out. DO NOT given them any more ammunition! Save that for when you are interviewed for your next job - it's OK to talk about the increasing and unreasonable workload, but do not mention anything about your supposed "attitude" or "behaviour" (they were out of order there, so don't bring it up - an interview is not a therapy session).

Find out what your notice period is - it's often the same as your pay period, eg 1 week, 1 month. if you're unlucky it might be longer. But you can go sick, then resign. You may even have holiday pay owing to you by the time you actually leave.
If you don't go off sick, and you do go back into work, do as others have suggested - the bare minimum. No extra hours, no working through lunch etc.

I'm sorry this is happening to you, but hold your head up, OP. You are better than them, you have a way out, you can handle this! You'll look back in 6 months months and ask yourself why you put up with it for so long!

Those figures are most likely made up of unfair dismissal, which is a lot easier to prove rather than constructive dismissal.

Leave on your own behalf and then you would have to claim constructive dismissal, rather than staying put, being let go, then filing for unfair dismissal.

Companies are a lot more likely to settle a claim for UD, rather than CD.

To lighten the mood...

I’ve only read OP comments - please contact ACAS before you resign.

In your position I would build up my side hustle (pilates) and also look for another job. In the meantime I would also be doing a bit of "quiet quitting" as you employers do not value you. Cut back to your basic hours and slow down, so that things begin to pile up. Rather than trying to cope with the extra workload allow it to slide. Look busy but take your time. When your manager whinges tell them you cannot fit in the extra and ask them to prioritise the tasks they want you do. Put the ball back into their court. The fact that they will not increase staff is a management problem. not yours. Use the time you gain to study up for your pilates instruction.

I was in a similar position when I decided to leave my job for uni. In the final year I cut out all the work I had previously did at home. We were being asked to do more and more with less and less so I just allowed things to pile up. I had an appraisal and my manager suggested I was being less productive than I have in previous years. I agreed with him and told him that I was concentrating on what I saw as the essentials. If people in other departments were whinging for things they reckoned I should be doing then they should get up off their asses and do it themselves.

I had used the extra time I gained for my university prep. and resigned a few weeks after my appraisal. I had already sorted my reference for uni so I did not need to trouble my boss.

I would resign but get signed off with stress for my notice period.

Fuck em.

The figures are for unfair dismissal including constructive dismissal. The ET1 form (the form that claimants submit to the tribunal) doesn't separate the two forms of dismissal when making a claim. Whilst constructive dismissal relates to breaches of contract, and unfair dismissal relates to the way an employee is dismissed, they are referenced together as "unfair and constructive dismissal" by Gov.uk.

Constructive dismissal is unacceptable treatment, making it impossible to continue working. Common examples include:
● Non-payment of wages
● Demotion or reduction in responsibilities
● Unilateral changes to pay, hours, or job role
● Harassment, bullying, or discrimination
● Undermining trust and confidence (The implied duty of trust and confidence is breached where the employer, without reasonable and proper cause, conducts itself in a manner likely to destroy or seriously damage the employment relationship)

Go of sick and stay off until ever second of sick pay is used.. Then leave.

Leave.
It's a no brainer I would think.
Surely you earn more than minimum wage as a pilates instructor? And it is something you enjoy?
You could work less hours for more money.
I can't imagine why you would stay.
I'm desperate to find a pilates class with a 'live' instructor who can tell me what I'm doing right or wrong. not a blinking les mills or whatever it is programme where if you are new you are simply lost.

Wtaf!!!!! Sick line for a while, until you find another job

These days in offices everyone is expected to be ‘pleasant’; it’s no longer enough to be good at your job / do more than your fair share etc. Anyone who isn’t ‘nice’ gets a minus point even if they are competent. If you are ND /introvert it’s hell. WFH is a blessing for this reason alone.

given your job is min hours, you should find a low-responsibility easy job that does not stress you out but makes you happy.

It is a good idea to go for constructive dismissal as many places would rather settle out of court rather than get any adverse publicity. Ages ago a lady went to an IT as Morrison's were changing her job considerably. She won and some Chief Exec said he may well put in a counter claim. I wrote to him and said if he did that I would ask 10people I know to boycott the shop and ask them to do the same. I forget the lady's name but she set up a company helping others going to an IT. The man didn't reply but left Morrison's rather quickly. I said to him he might think one pensioner cannot do that much but I told him my plan. I was rather amused it was in the press just a few weeks later that he was looking for .a new company . I meant to let the lady know but as it was Morrison's didn't contest it. I often wondered why. I use the same technique with those shops that fired staff for intervening with theft. It is surprisingly quickly that I get responses from Chief Execs who obviously get into panic mode when given the details of how quickly contacting 10 people will multiply. Ages ago the Guardian asked for people to contact Waitrose as they held an innocent man who was a carer for his Mum. This time it was near Christmas and I wrote to him and said I am a pensioner and have not done my shopping for food or presents and would be spending money I had saved. Lots of people apparently did the same and the man got an undisclosed 6 figure sum later. People pressuring firms does work. All the best OP and it would be lovely to hear how things went. The lady from Morrison's went on holiday as well as set up her company. Big businesses think they will win but often don't and I love being just a small part in it and love finding out they settled or did a deal out of court. I don't run a website as being anonymous often works.

Longer term, I would personally look at leaving but, if sick pay is reasonable, I would be signed off sick. This is to buy you some time to seek any legal advice about their behaviour - constructive dismissal etc and to look at alternative jobs etc.
It takes the pressure off to make a decision in such a toxic situation!

Sometimes going the contesting root is not worth the stress and hassle.
Think about saving your energy.
Go out sick with stress immediately and drop them in it.
Focus your energy on a new job and your pilates business.

I'm glad you seem to have found your anger and not feeling upset. You were spot on to basically tell them it's not your job to sort out their issues. "Solutions not problems" comes with an increase in pay and responsibility.
Good luck finding a new job.

What horrible people you work with.

Good luck on finding a new job.

Exactly. When I worked in retail and we had visits by higher ups they would keep me out of the way because I was never afraid of answering their questions truthfully instead of pretending it was all lovely. To be fair it was a good place to work with not many issues but if you don't want the truth don't ask me what I think.

Is it possible to do only do your own job if you are so short staffed? They have properly shot themselves in the foot if you can but I'm wondering if it is possible in practical terms to not provide the extra cover? It's a ridiculous situation in a minimum wage job to be expected to do what they are suggesting you should.

I’m glad you didn’t hand in your notice. You will have more rights having been there a long time than you would starting again somewhere else and it is hard to find something else as a woman in your fifties.

God, they are arseholes.

I had exactly the same when I asked for examples of my 'behaviour'. Twisted truths. It's shocking really.

I was fired but how glad I am now! I see and speak to ex colleagues a lot and 7 years later the same stuff is still happening, the same bullies are still operating in the same way, men are still revered and excused and women picked apart.