Cancellation not possible with Vodacom

I cannot cancel my contract (when it was expiring) and unable to speak to a human in this regard. AI is useless and does not address the matter. Have gone through the process to cancel - received a cancellation form, which I signed and returned (ref. no. below). This was acknowledged and I was informed later that the matter has been dealt with. This did not take place as I am still being charged. Would leave Vodacom, but am bound by a contract I did not agree to.