Forced to keep a contract I no longer want and billed for it

In August 2017 I called to cancel my one contract number is ********** and I was told it's cancelled. Fast foward to November 2017 still it has not been cancelled and no one can explain why. But they still not cancelling and I am being billed for it. And the amount has gone higher for some reason unknown to me. I called retention number 084143 and no one has been able to assist numerous times. I even called whilst at the Forest Hill City Mall Cell C shop and no one could assist.