Debit on an account that was declared closed

i settled my Game account in full contacted the Game customer care and paid the exact amount, i signed the cancelation letter at Game Jabulani mall same day when payment was done and letter was scanned and emailed to have account closed. to my suprice last month of September my bank account was debited ???? how do u debit an account that has .00 balance . i contacted the customer care and i was told its my fault that they debited as they did not get my letter and that i did not write another letter requesting for debit order to be cancelled, how many letters should be send through to have an account closed, I want the amount debited inmy account credited back i want a confirmation letter send back confirming credit has been done and account closed and no debit will never be send to my account, i requested this letter a month back still nothing not even a follow up call, spoke to Alia and Shaun team leader refused to take my call the spoke to Mikaila Martin. I WANT MY MONEY AND DEMAND THAT LETTER TO BE SEND. the service is really shocking .