Account debited after settlement

Price n pride contacted me on the 7 Nov 2014 to remind me about payment for end Nov. They said the call was recorded. I asked them not to only debit the monthly installment but all the money I owe them at once. I made it clear that I do not want to owe them anymore. The settlement amount was R4157, and indeed they debited it as agreed. I went to Phumlani Mall brach in Dec 2014 and my account was on zero. Guess what on the 29 Dec 2014 my bank account was debited monthly installment as usual though the account was settled. I went to Phumlani Mall Branch to ask what was that money for? I was told that it's the money I owed. And I asked if it's possible to owe after settling the account? The answer was only Head Office knows. Head office didn't answer the phone so I was told to come again the following week to check if head office responded to the sent query, really?6