Bad service

I have been trying to cancel my contract since October 2019 to extent that I have resorted to reversing their debit orders and now they keep on changing their reference number when debuting. I have tried calling and have sent communication cancelling to no avail. I went to a cell c branch and was told that there is nothing they can do and they suggested I call which gas not worked previously. I really need help as this is ruining my profile with my bank.