University fees issue- thousands outstanding! Where do I stand?

[SneakyLilNameChange]

I have been doing a masters for years and am finally completing it having APEL’d in some units from other units. This academic year I am doing a 30 credit unit and a dissertation. Most of the other units I did while working at the uni (I left in 2023) and was told these would be funded by my department.
In sept had to register for this academic year and pay fees of £2500 odd- fine, done. I have an email from the department saying my anticipated fees for this year were £4600 total so i assumed I’d pay the remaining £2k odd this term however I had an email saying I need to complete registration and pay £6750?!?
Obviously I contacted finance at the uni to check and they said yes- this years total is £6750 and my previous payment had just covered outstanding fee for 22/23 (when I worked at the uni).
Again I’ve contacted my department lead and she’s passed it on to internal finance with a bit of ‘hmm who said you would pay the lesser amount and we will see’ and now I’m panicking- I cannot afford £6750. Effectively they’re saying I haven’t paid for the unit I’ve now done and submitted work for which has taken hours.
I have an email from the admin saying the £4500 fees which I will send and my previous manager knows funding for the masters was agreed. Do I sit right and refuse to pay any more than I originally thought I’d need? How does it work? Unis are sooo disorganised it’s literally the department paying itself which has gone wrong. And if they thought I owed fees from 22/23 why wouldn’t they have chased this before now?!

We have a policy at our place which is along the lines of you have to stay working here for 2 years minimum after you graduate or pay back the course fees at a % of how many months under 2 years it is. So if you stayed for 1 year you would have to pay back 50% of the fees. That should have been made clear up front before you started your course though.
I would get onto the student union for advice and challenge the invoicing for fees from 2022/23 and not making it clear exactly what you were paying for.

@Justkeepingplatesspinning I understand that but nothing like that was ever mentioned!

In which case there should be something about a fee waiver that you got at the time with your offer letter? It's going to be tricky as you've not got access to your staff email, but suspect that would have been sent to your personal or student email? Time to start digging out all the paperwork so you can fight this. Were you in a union when you worked at the university? As well as the student union, they might be able to support you. Not sure though, if you're not a member now. Worth asking as you've nothing to lose.
Good luck!