Incorrect Billing and Forget signature

I signed a 2 year contract with planet fitness indicating that I will pay R318.50 per month for two years.<br> I paid cash for my first year to avoid any payment issues. At the beginning of this year I went to speak to the manager to request to pay cash for the year again and was not permitted to. I refused to give my active account details as the system did not indicate how much I would be billed. When the second year billing information appeared, I saw that I was being charged R550.00 per month for my contract as oppose to the R318.00 that was signed. I raised this issue with the manager and a month later they retracted the R550.00 and it did not appear in the billing. A month later two amounts of R550.00 appeared, which I raised again with the manager. This matter was not solved and the manager eventually left the club. I had to start this process again with the new manager who then printed me a form with a signature different from mine agreeing to R450.00 in my second year. I was promised that this matter would be solved and the billing would be corrected and decided to pay until September. Today I received a call from dept collectors saying I owe planet fitness money.