Cancellation not being processed

I have been caling to cancel my data line/contract since September 2015 and to this day it is still active and MTN keeps billing me. I called in September for the first time as my contract came to an end in October. I was advised to call again in October to make sure. When I did that I was not cancelled. I called again in November and was told it would be cancelled and was given a reference number. Once again I was billed in November and the line still active. Called in December was given the same story and process with a reference number given each time. I checked again in January after being debited by MTN and they still hadn't cancelled the line. Called on 6 January and was told the line would be cancelled and it wasn't. Called on 15 January and was told it had been escalated to the manager of the department that deals with cancellations. It is still done not done after calling today. I have had it!!!!!