AVIS Card Auth slow to clear

FNB Is the most horrible bank to bank with slow on processing card Auth. I have rented a car with AViS mid February and returned the car 2 March and my account was debited on the 4th March by Avis. That leaded my account to be on a negative. Today as we speak the Auth is pending. Have contacted Avis and I was told the cancellation was sent to the bank. Nothing. I really hate banking with FNB. How could you pay something and not clear the Auth. I need answers as soon as possible. I am moving away from this bank .