MTN continues to abuse its clients!!!

I phoned mtn a month ago to cancel a contract with mtn, after waiting for about an hour for an operator to answer. Guess what, I got a call again from MTN, asking me if I would like to upgrade to a 24 month contract as they have no record of the cancellation. And another inflated account today! What more can i do to cancel this contract? Does anybody out there know so I can be informed?