MWEB cancelled contract still being billed

I cancelled my Mweb contract in August 2021 and was quoted a fee to settle the contract, which I paid as per the details I received. For the last two months my bank account has been debited with the premium which I have reversed and sent emails to query the issue with the Mweb accounts department. Now I am getting threatening messages that I will be listed on the credit bureau for bad payment. This will not do.