cell c has been debiting unnecessary

Good day I have been experiencing a major problem regarding the accounts department in cell c they have been charging me R637 for a contract that has been paid in full, I have paid the cancellation fee in november and it will be only debited once but the same amount has recurred again this month, I have been in contact with the call center they keep reffering me to other departments and the johannesburg head office of cell c seems to be always busy and no luck of getting through anyone in higher authourity to sort out the issue, please if anyone can assit on how to resolve this issue contact me on ***