Overcharges after the fact

I traveled to South Africa with my wife in March. We booked a Europcar through American Express Travel Services. We were quoted a weekly rate for the car to be prorated over four days with no additional charge for drop off at a location outside the airport. American Express covers the Liquidated Damages Waiver if you use their card. When we arrived at the Johannesberg airport to pick up the car, the Europcar representative told us that they do not honor the LDW from the credit card company unless we had a letter from American Express, which we did not. They charged us for a mandatory LDW, and even though I told them that I was the only driver, they charged us for an additional driver. They did not provide a copy of the contract I signed and they refused to provide an accounting of the charges when I dropped the car off. I was billed double what was quoted initially. DO NOT RENT FROM EUROPCAR. They quote a low rate up front and then pad the bill at the end.