Cancellation of Accounts and Overbilling

I cancelled my contract on 16 Jan 2016. They said you must give a months notice, To date contract still not covered and they are over charging me. I called numerous times about my account, call centre constantly say they have logged a request with finance and back office and will revert back to me within 7 days. Nothing has been done about the account and nothing has been done about the cancellation. My bill has now doubled for 2 consecutive months. Seems like Telkom likes taking people money, what happend to putting the customer first