Issue to cancel contract

I was due for upgrade and my contract was paid up in full. Due to fact they didn't have the phone I want I cancelled the contract in store... They made me sit and talk to cancel department on phone in October 2017. In November I got a bill and I paid it. When I got a bill in December I phoned to find out the contract was never cancelled. So I cancelled again. It's January and it's still active. Plus i am in arrears now and will have a bad credit rating. To top that off.... I need this number to be ported so my customers can get hold of me... I've lost thousands do to cell c. I haven't used cell c for November or December but I get billed although I cancelled twice. So am I just going to cancel everymonth and get bad credit rating... Ohhhh wait I can't cancel if my account is in arrears... How convenient.