I had a similar situation with Avis last December. I rented a car in Des Moines for a week. I used my corporate AWD code when making the reservation on line. When I returned the car, the charges were about $75 too much and they had charged me for mileage driven above 100 miles per day. My corporate AWD provides a discount and unlimited mileage. I immediately complained and the agent at the counter reran the billing with the corporate AWD. I also had a printout of my on-line reservation to back up my claim, but it was not needed in this case. Since then I have had another incident of the AWD being changed but the discount and other benefits happened to be the same as my corporate AWD so I didn't bother to ask why it was changed. The morals are, (1) always know what you expect to pay and the codes that get you to that price and (2) always get a written or printed copy of any reservation you make showing the agreed to price and codes and have it with you.