Thrifty Rent A Car

We rental a mini van and when me and my husband arrived we went though the regular stuff but then we were informed that they charged an additional driver fee of $100, we then informed him that we would only have the 1 driver which was my husband. We didn't budget for that extra cost so after talking back and forth the clerk made the suggestion that he can cut that price in half. So we agreed after the contract printed out and we signed we noticed the charge was still at $100.00 so we asked the clerk and he said oh when you return the car the correct charges will appear? So we believed what he said and went on our way. After returning the vehicle on the return day we dropped it off and left. The next day I looked at the receipt and noticed the charges weren't discounted like the sales clerk had promised? I call the customer service office and was informed that they were NOT going to return any fees and it was our fault that we did not get it cleared up before we signed the contact and that there was nothing we can do except eat the charge? I will never ever rent from them again!