Cell C account cancellation and potential *****

I have been trying to cancel my contract with cell c. I have been on the customer care line for ovee 50 minutes trying to get support after (1) i tried to give notice on this contract via the app (2) they sent a text message to say that i need to call the customer care line (3) i called the customer care line and after 50 mins on the call for them they insisted that they could not action the cancellation because they cant verify that i am the cusyomer. The law only requires me to give notice to cell c. I am not aware of the security question ni am failing despite THEM calling me by my surname. There seems to be no confirmation that i am the client despite the contract being in my name and the monthly deductions coming from my account. I am now referring this to my banks ***** department because Cell C is deducting money from my account despite being informed to stop the contract.