Impossible to cancel vodacom contract

I am trying to cancel my vodacom contract but it seems to be an impossible task. The call center is either dropping your call, or when you do speak to a consultant and they find out it's about canceling they put the phone down in your ear or not answering. I visited the vodaco shop at woodlands mall and they are refusing to do it as they claim they are not allowed to do it any more. So how do I cancel my vodacom contract.