MTN makes it difficult to cancel a contract!

I have tried to give notice of cancelation for my MTN contract, which expires next month. If you go to the MTN website, they tell you to phone 135 to give notice of cancelation. This number rang for 45 minutes with no answer? They also provide an email address: ***, however, the reply from this email says that you cannot cancel contracts over email? How do you actually get to cancel a contract when they make it so difficult to give notice?