Unauthorised debits

I havr a serious problem of unauthorised debit ordered since Nov 2017. When i go to the branch they tell me that the is nothing the bank can do to stop those debit orders but i must talk to the company that debit. I mean how can i talk to a company that i dont even know. I have been banking with fnb for about 13 years but now i think the only option is to cancell my fnb account because clearly fnb cannot protect my money