Still Waiting for My Deposit!

We have been renting a car from Sani Rental Car in Pretoria for over 6 months, and with EVERY RENEWAL, they charge us an additional deposit on top of the rental fee, claiming it's necessary because the driver 'changed.' According to them, this amount is supposed to be refunded by the bank within a month, but we haven’t received any refunds for ANY of the months we've rented so far. We are calling the shop EVERY day, and they are not solving anything. They told us to contact the bank, but the bank has nothing to do with it—it’s Sani that needs to return the money. We don't know what else to do, but we definitely DO NOT RECOMMEND this car rental company!!!