Forcing me to upgrade after cancellation

Good day, I had a data contract with telkom that I took in december 2018 and I called and cancelled aft er two years when I started receiving calls to upgrade. How ever an upgrade was done without my authorisation. My initial contract was R170 when it ended telkom started deducting R99 from my account that I reversed. I contacted them but they failed to give me. I sent a complain on their website and I received an email that says they will attend to it and come back to me. Which they failed to do. Now they are threatening me with credit bureau. My record is very clean but they want to damage my good credit status. Please help.