Cancellation of a contract that has come to and end.

I have been trying to cancel my MTN contract that has come to end of life after 24 months. They let me hold on for hours and then cut my off.... If they eventually answer, they keep on transferring to another department only to cut me off again.. After 2 months I got it cancelled, but they did not update on their system and now my account is on out to data charges, and I have to pay triple my account. Trying so resolve this and get a refund from MTN is mission impossible.