Impossible to cancel an expired contract

I have been trying to cancel a data sim contract which expired 12 months ago and continued month by month. I first was told there is a contract cancellation fee. When I asked for proof that I renewed the agreement I was told it would be cancelled. A month later and no cancellatiin yet. The latest now is that I can pass the security questions via customer service, but the terminations department can't get me verified. I have asked on 2 occasions for a manager to call me. But they hide behind inexperienced and untrained junior staff. Customer service is non-existent making a mockery of their vision statement. After more than 10 years I am now moving my entire family's contracts. I am willing to pay a premium at another provider as I will never do business with cell c again.