Contract cancellation

I was offered a contract deal two years ago, the Lap top was delivered on time but the sim card was faulty. I called customer service they told to go to the nearest branch when i got there i was told to pay R180. I refused to for the number i haven't even used it was not my fault that the sim card was faulty. I decided not to use the number i paid for the contract for two years. In August 2015 i was offered an upgrade that's when i told them i do not want the contract any more. They told me it will take a month to cancel, i called them again end of September they told me the same story and when i called them mid October they told me my bank account wont be debited to my surprise i was debited , when i called to query they told me is for the data they sent me but i did not use that number not even once i have been paying every month for two years did not even skip a month for a faulty sim card now is a mission to cancel it.