Cancelation of Mtn wifi contract

I have been trying for days to get my contract which has already passed its term cancelled with no joy at all. Everytime i phone in they make me hold on for 40 minutes or more or their system is offline. Its like they dont want to help. I have even went into a store and been told that they cannot assist i must call 135 on my own. I have wasted 100s of rand on airtime not to mention my time at work. My contract is now on month to month. I cannot afford this anymore. The number in question is ***