Unauthorized debit order.

When I was going through my bank statement I noticed an unauthorized debit order with the reference Shaprit RAP187918. The most irritating thing is that there are always such debit orders and FNB does not seem to try and help us as customers with these. And everytime you reverse this you have to pay a certain amount. How is it possible that a debit order is made without my approval as the owner of the account, and what documentation is used to make this happen? I am really getting fed up with FNB because when you inquire about these transactions they can't give you a valid answer.