Furious with FNB. You robbing your customers

I am absolutely furious with the pathetic service I keep receiving from FNB. I have to repeat my same complaint so many times since Oct 2021 about a cancelled debit mandate which is cancelled with the service provider and I have a letter confirming this, yet every month they still try debit my account and I always landed up having to pay these unpaid fees. I have had enough and will close my check account after more than 12 years of banking.