Very Bad service from MTN

Trying to cancel a contract number the last 3 months. Everytime i phone and they say they put it through for cancelation and then comes the end of the month and deduct R100 more because the number is running month to month. But i am trying to cancel the number the last 3 months and it is like they don't know how to cancel the number or they just robbing the people for money as every month they taking more money. Please just cancel the number.