How can I cancel my contract and why do MTN call it a call centre?

If I could give no stars that would be more accurate. I have now tried 4 times to unsuccessfully cancel a contract. They obviously keep on billing me for it and taking the money (I suppose *****ing might be legally too strong a word) even though that number has not been used for more than a year. The call centre (it shouldn't be called that but rather the UNISA helpline as they keep on telling us about how UNISA students can get airtime) never allows you to get to a call agent and keep on sending you back to their UNISA messages. The few times you actually get through, they promise to cancel the contract but to date and after cancelling it four times, it is still active. Pathetic!