Vodacom tired

I just have no luck with Vodacom changing to a respectable, trustworthy company any time soon. I was phoned by a consultant from Vodacom, in January, regarding its time that I can do an upgrade, to which I app**** I am not interested, at the end of my contract term I decided to cancel my contract with Vodacom. The consultant actually convinced me with a good package to stay with Vodacom and do an upgrade, to a certain amount I specifically said yes to. When I received my new invoice after the upgrade, it was double the amount than what I was told my new payment will be. It has now been a week after I had to phone them, be on the phone for hours, getting transferred from one consultant to the next, and still a week later I am still waiting for confirmation that the upgrade has been cancelled and that my invoice be changed to the CORRECT amount. What must I do as customer to get the appropriate assistance, from the right person, to fix the problem that they caused, not me!!!!!