Bad customer service

I had a cell phone contract with #CellC. I canceled after 2 years because I no longer needed it. It was paid up. I have sent emails to cell c to cancel it. I have had confirmation that it's canceled BUT every month they debit my account with various amounts. I reverse it and get charged banks charges for it. I can't get hold of any one to sort this out because no one follows up and closes this account. They harass me to say the account is in arrears which affects my credit. Every month the amount varies. The service is pathetic!