DOUBLE CHARGES ON OVERDRAFT FACILITY USE FEE

I USED FNB OVERDRAFT FACILITY FROM 1st TO 11th AUGUST. THIS WAS CONSIDERED AS TWO MONTHS USE. REASON GIVEN "MONTHLY SERVICE FEES ARE DEBITED ON 3RD OF THE MONTH. WATCH OUT, I PAID TWICE THE USAGE FEE ALTHOUGH MY ACTUAL USE FELL WITHIN A MONTH. I CONSIDER THIS ********* BY THE WAY, FNB PRICING GUIDE CLEARLY SAY YOU ARE CHARGED USAGE FEE FOR THE MONTH YOU USE THE FACILITY