Best way to recover money?

I live in supported housing and my appointee pays monthly for my 5th of the house bills which is about £135 a month, it used to be £230 a month and I was paying that for nearly 8 years. It transpires that the company have £6.500 in the shared bills account which I believe that is a 5th of my money. After repeatedly asking my supported living manager how much I have in the shared account she keeps saying not a lot. Which is false as I've seen the bank statement. How can I get them to give me back my money? What rout can I go down?