Debit order reversal trauma!!

I have an unauthorized debit order that debits my account every month since March, I have tried reversing even asked the staff member at their Benoni brach if it’s possible to stop this debit from going through seeing that they unable to to reverse it and was told I had to contact them myself!!! How do I contact them when I don’t know them? The debit order does not show on my debit orders but it debits every month on the 25th