Telkom incompetance

I have cancelled my LTE contract with immediate effect on 29 August 2018. The operator still asked me if I want the debit order to be deducted and I informed her "no, because I'm busy installing fibre". On the 5th of September Telkom debited my account, which I subsequently reversed. I also did not receive any new data from the 1st of the month, which confirmed that the contract was cancelled. Now I get a notice that they want to blacklist me for payment default? Seriously???