MT Refuses to cancel contract

In November I did an upgrade with MTN, but due to their poor service or lack of rather I decided to cancel the upgrade. I asked them to cancel my current contract as well, and they should tell me the full amount owing to them. The sent me an SMS confirming how much I owe them and informed me that they cancel the contract. I am now in my second month and MTN is sending me a bill claiming that I owe them money. I have called the call centre literally over 10 times to cancel this, and I have still not received any response. I am beyond furious as I do not know what to do, I have instructed m y bank not to allow an y debit order to go off for MTN as his is now an ******* request. They loaded airtime on my phone on the 14th and I called them the same day to ask them to take their airtime back. I think the only way this will be resolved is if we get the Ombudsmen involved as MTN refuses to cancel this contract.