HERTZ Hertz charged me extra "fuel service" while I returned the car with full tank oklahoma city, Oklahoma

I traveled to LA and rented car from hertz, 2 weeks after my trip ends, Hertz sent me a letter addressing that they will charge me "extra fuel service" (which is $75.08), they said it's because when I returned the car they need to fuel it with 7.79 gallons. This is totally a bad that you would only think a bad company would do, I never expected that hertz, as a big company, is doing this trick to its customer. I filled the tank, I got the receipt, and they still trip to rip you off!!!!
My rental is around 6 days, in late August in 2011.
My first name is Charles, last name is Pang, I live in Plano Texas, 38 years old. I am reporting this because I don't want other innocent people to go thru the trouble. DON'T rent cars from Hertz! At least, I will never do that again.