OVERDRAWN ACCOUNT FEES

FNB KEEPS ON SENDING ME MESSAGES THAT MY ACCOUNT IS OVERDRAWN WITH R773.32 WHERE WILL I GET THAT MONEY AND YET I MUST MAKE PAYMENT IMMEDIATELY I WANT TO KNOW HOW COME MY BANK ALLOWS DEBTS TO GO OFF WHEN MY ACCOUNT IS ON ZERO RANDS PLEASE EXPLAIN THAT PLEASE YOU AS OUR BANK NEED TO STOP THIS WE ARE ALL STRAGGLING TO MAKE ENDS MEET WE PAY FOR EVERY TRANSACTION NOW THIS ALSO NO MAN THIS IS NOT FAIR MORE SO ON PPL EARNING LESS