Debit order reversal

There is an amount of R 1 336.01 that was debited from my account on the 29/04/2020 by means of debit order. I contact FNB and even write an email to the ceocomplain email address only to be told that they are unable to reverse such a debit order and their reason was that due to Covid 19 some consumer are reversing valid debit orders because of financial constraint so I was advised to contact the service provider. I explained to FNB consultant that I don't know who those people are (the service provider) and I don't even have their contact details and there is no history in my account of such kind of a debit order.

Kindly assist