Over charging and not canceling contract.

I have been a customer of Vodacom for many years but now I had enough. I have phoned the cancelation department twice to cancel a expired contract. Guess what? They did not canceled the contract. I have mailed their customer complaint department and even have cc their CEO. They contacted me later the day promised to come back to me later the same day its been more than 2 days now. I have mailed them again but no response. I even have picked up now that they are over charging my combined account. What steps can I take to get this resolved. I am at this point of canceling all of my contracts and move to a alternative service provider.