Discovery Bank committing *****

I have paid up and closed my Discovery Credit card (Reason is another story). 2018, I was promised the account would be closed, I needed to wait cause they accidentally took payment from my FNB account to pay off an already paid up credit card. A year later, trying to call a call centre which cannot call you back to resolve their mistakes, I tried again. After multiple attempts finally they responded in 2020 that the account in now closed. Thought finally I am done. A few months back, this is now 2021, I see bank changes on my FNB account for Discovery credit card fees. Tried to report to FNB that the debit order is **********, this went no where. My only way out was to stop the debit order and pay FNB to do so. Now I get at least 3 threatening emails every month demanding payment from Discovery on a closed account.