Vodacom Fibre is a Nightmare

I cancelled my Vodacom Fibre package due to a relocation. I submitted my relocation request beginning of April 2019, and we concluded the matter on the 15th, with an agreement over mail stating it will be cancelled. They sent me the quote which clearly states that a Zero Balance, which I accept by signing and send it to them. Also I call them for an official cancellation of which they process, all the way till the 30th. Now I have been handed over to Collectors (Burnardraaff), they are saying I owe Vodacom, as their billing ran even after the cancellation was processed, and now I am being forced to pay, even after providing documents and mails proving an incorrect billing. My credit record is being *****ed due to negligence and inability to rectify accounting errors. This is not the first time Vodacom messes up and fails to acknowledge fault.