Vodacom refuse to cancel contracts

At the Vodacom store in Centurion they informed me that to cancel a Vodacom cell phone contract this needs to be done via a phone call. I have been on the call centre line for more than 45 minutes with consultants trying to cancel my contract. They keep refusing and keep offering me a alternative deal. When I refuse the new proposals they just drop the line and I must start again. No e mail is available to address this in writing.