Cell C bad service

Cell C delivered a wrong phone to me, I returned it back via Ram courier company, they confirmed receipt of the cellphone and the contract was cancelled. To my surprise Cell C is still deducting money from my account, it has been two months now still the contract was cancelled. I have since requested that they refund my money back, but to this day I haven’t recieved my money. Everytime when I call, I am given a new reference number and I am told that they are flagging my case to be reflected as urgent and I will be called within few hours, no one calls, I think I have made over 20 calls now. Whenever I call them, they are telling me that they are waiting for my bank statement, and I have sent it to them several times.I have run out of options because I have go nowhere to go. Even this month they will still deduct my money whilst I don’t even have their cell phone.