Disappointed with mtn

I am so disappointed with mtn during my last month of paying my contract well the cancellation amount I was not debited which use to happen every single month but this time they did not. I then did receive an statement saying I need to pay the following month with an added 100 to it and on a different date which is before my pay date once I call my calls get cut and once I sent an email on my concern I don’t get a response.