Struggling to cancel my contract

My contract has ended and I have been calling mtn contact centre to cancel. When I call they transfer me from this department to that department with no assistance. Some even hung up when I mention the word cancellation. It's funny because they do call me to upgrade my contract but when I mention that I need assistance with cancellation they hung up. I really want to cancel as I am not even using their sin cards. The account has now accumulated fees which I have settled today but my fear is they'll add more charges. Please assist with cancellation. This is now frustrating.