48 hours turns into a week!!!!

On Friday 22nd of Jan I hired a car from avis in Grahamstown. The agent Apollis explained to me that there will be a hold on my acc for a certain amount. He also said that 48 hours after I return the car it will be cleared again. Well it is now Thursday 4 days later and it is still not cleared. After I went into Avis again to ask about this he informed me that it would take another 48 hours which will put us into next week!!!!! This is unacceptable service and surely Avis cant just get away with this???? I would have liked to hire a car from them every Friday,but not with this service I am receiving!!!