Nedbank withholds funds from clients without client permission

I used my debit card for a car rental with Avis, who place a hold for a security deposit on my debit card. After returning the car, within 2 days Avis had settled the invoice and released the hold status. But Nedbank after 5 days has not yet released the funds back to my account. I consider this an ******* act of withholding funds that do not belong to them.