MTN contract cancellation

I have been trying to cancel a MTN contract since March. It was due for upgrade on 10th May. Beforehand they phoned me twice about the upgrade and I told them I wanted to cancel because I had singed a new contract with a new smart phone and number. They agreed that was in order. Come 10th May and my contract was not cancelled. Since then I have phoned 135 countless times and cannot get beyond the menu options. I have phone *** three times and after an hour of holding the call is terminated. I have contacted them twice on their website (refs ***, ***) and received only automated e-mail replies. The number I am trying to cancel is ***. MTN has the worst customer care of any company I have ever dealt with. When my remaining three contracts are up for renewal I am changing providers.