Contract phone

I had a contract phone with cell c for 24 months, as per the contract I was supposed to finish it end of August 2019,but last year October I settled my account and my contract was canceled. After a couple of months Cell C started to deduct again and I kept on reversing the debit order.then I went to cell c shop in Bayside Mall to report the matter,they called their customer service and the settlement amount appeared on their side,but they said I didn't phone them to cancel the contract of which one of their employees called customer service to cancel infront of me.so they said they will listen to the records and get back to me.now it's more than 3 months, they never get back to me and they still deducting and this thing of reversing their debit order is affecting my credit record