Still being billed for cancelled contract

A couple of months ago I called Vodacom to cancel a data contract which was suppose to be cancelled this month. After I was told the initial contract I was sold was a fixed term contract instead of a month to month contract I thought I had signed up for. I've now waited for 24 months to cancel this contract but two months on after numerous calls i'm still paying for this contract. surely there must be some recourse with these operators that hold the consumer at ransom.