Car rental

I rented a via rentalcars .com at Trifty. When I arrived at Thrifty desk at OR Tambo International, I was told that I don't meet their requirements to rent from them, therefore rentalcars.com must refund me the pre-payment I made to them, they as Thrifty they don't get involved. It is a hussel to get hold of Carrentals.com over the phone, once you get hold of them they are rude and not helpful. I just want me money back from these two companies