Vodacom refusing to cancel contract

I am very much frustrated with Vodacom. I have a Vodacom contract since the past 8 years. I know want to cancel the contract and go on prepaid. I am trying to cancel my contract for the past 2 years nd with no success. Each time I call the cancellation number I am told that I am on the old M5 system or something and I will be called. I have never received any call. I went to the Vodacom stores and got told I have to call that number there is nowhere I can go to and no other way to cancel the contract. Not even an email address. Come on Vodacom cancel my contract and put me back on prepaid.