Pay account but still owe over R3000

I went to Game is Centurion Mall on the 11 March 2014 to pay off my account, I have the slips to prove this. Almost a year later I have to find out that my name is black listed and that I still owe them over the R3000.00. I phone them on the 30th to find out what is going on and was advised that I need to get a letter from the Head office to state that my account has been paid off, after 7 calls and 7 different people I was advised that the letter will be sent to Saturday. Well its Tuesday and I still have not received the letter. My name is still black listed and all this because I paid my account but they did not do their work to clear their records.