Delay on deposit refund

Avis in Stellenbosch was amazing to start off with, but the issue at hand is the fact that they're not paying back my cash deposit and when I phoned they apparently had the wrong account number so the payments keeps "bouncing back" was their words. This makes no sense and I know for a fact I provided the correct account number which means they made an error when capturing the data, its been 12 business days since I returned the car.