Cancellation of a sim contract

I'm not happy with the service that I'm receiving with the MTN call centre, I have been trying to call a million times! to cancel my sim card contract with no luck. its either the calls will be ringing for a long time with no answer or be picked up only for it to be hanged up on me without even helping me,it is really frustrating as I've been trying to cancel this contract for over a month now. This is really unacceptable I have been a loyal customer with no problems only for me to treated like this!!, I want this matter to be sorted as quickly as possible, my email address is *** or call me on ***