MWeb and Telkom - I should have known better

Since the beginning of this year I have been getting invoice amounts that I do not agree with, I call the centre after which I'm told they will review the billing, they then send me a new invoice showing that they have reversed the amount, a few days later that amount is requested from my bank account, which then comes back unpaid - this affects my credit record negatively. I've called the accounts department on many occasions but still this cycle continues - I'm even being billed for boosters that were bought in November, which I totally disagree with. The data on the boosters lasts less than a wee**** I'm at my wits end with both MWeb and Telkom !!!