MTN's horrifying service

Very bad service and communication from MTN. I cancelled one of my numbers with them and asked them to stop deductions of data and a airtime a month before contract ended. They went on to continue deducting, didn't confirm that the request was actioned, I requested the refund and none has been processed. What does one have to do to stop these giants from taking our money. I have tried everything in my power to stop them and get the refund but I am not winning.