Cell C - Debits your account just how they feel like it

Cell C, bills you (debit order), and then just turns around and say sorry, lets move forward. My contract expired at the end of April, and still billed me basically the same amount. They confirmed that this is due to extras - ie the whatsup bundle and insurance: WHICH by the way is/has been invalid for the last few months, so my device is no longer covered BUT they have been taking the money each month. When I asked the consultant how they could take money for insurance which is no longer valid, she just said sorry. If I had claimed they would have NOT PAID, so I am not covered and Cell C takes my money religiously for a device NOT covered. I am really not happy !!! I am the client how should I know that I need to cancel the insurance. When I got the contract the insurance was offered with the device.