FNB Personal loan debit before payday

I have a personal loan with FNB loans , I get paid on the 25th every month , this guys have decided to debit my account on the 22nd verry month ,they know very well that I get my salary on the 25th, why debit my account on the 22nd? so just yesterday they debit my last petrol money for the week before pay day. Do this people apply their minds when they debit!!! now my account is at zero and I don't have petrol money as Im waiting for the 25th payday