OP, given your struggles and ADHD, I am going to try to be constructive.
Firstly, you need to speak to Shelter. They are very busy so make sure you have as much relevant information to hand as possible.
Secondly, check all the tenancy deposit schemes to see whether or not your deposit has been protected. Yes, the landlord should have sent you the prescribed information, but let's not worry about that now. Someone linked that higher up this thread.
Thirdly, set up either an alert on your phone or, better still, a standing order to pay your rent monthly. That will save you from having to worry.
Fourthly, calculate how much money you should have paid for this current rental period and how much you have actually paid. You need to keep arrears down below 2 months to avoid a section 8 automatic eviction. Can you make sure that you don't owe anything by the end of this month?
You should have an up to date Gas Safety Certificate and Energy one (EPC?). Have you been sent those? If not, post here.
When you have done those 5, contact the housing department at your local council about whether or not you are living in a HMO. Maybe I misread your posts but it sounds like you might be. Rules for HMOs are stricter than normal ASTs.
Whilst withholding rent seems like the obvious thing to do, there is a very specific way of doing it. I don't think you are doing it correctly. Finally, this is not the best forum for housing advice. MoneySavingExpert's forum tends to be less judgmental and more constructive.