Incorrect Billing on my account

I have recently upgraded my contract with cell c. Last month I noticed that I was billed an amount of R687 which included insurance which I did not apply for. I reversed the debit order and paid via eft the actual amount. They then debited my account again with an amount of 441 which was the balance that I did not pay. I also reversed this because as I say I did not ask for insurance and it should not have been added to my account. Now my worry is that come end of the month, I will be charged for the insurance again and if I do not pay, they might suspend services on my account. I need his resolved, Please!