Unfair and horrible service.

I contacted Tempest Randburg to enquire the procedure for hiring a car without paying with a credit card. I was informed to book online just to get a reference number and I can make a payment when I fetch the car, or I can make payment online with a debit card. I booked online, made payment and got a confirmation and reference number. On the day I went to fetch the car, i was informed about the deposit for which was not mentioned, when I called, made a booking and when I paid for rental. Fair enough I got there and was quoted a deposit, which I was told that it will be refunded in full once the car has been returned. I paid the deposit, to my surprise the deposit was refunded but not in full. Why is there hidden costs that are not explained properly to customers, and the deposit should be displayed when making a booking and payment online. This is really unfair and frustrating. The experience was horrible as it is.