HERTZ RENT A CAR

I went through Priceline  and Hertz was the winning bid and then I decided to stay 3 days longer on my trip so had to make another reservation through Priceline and once again it went to Hertz.
  When I got to the facility, the line had around 30 people. There were only 2 agents working, and I think 7 or 8 video kiosks, but only 1 or 2 were available at any one time. The line was excruciatingly slow. When I finally was up I chose the kiosk. As I already had a reservation, it went quickly from there. I paid for the gas fill up since it was less than $70 I figured it was worth it.
 
Since our 2nd reservation was also with Hertz and the type of vehicle was the same, we called to see if we could just extend the rental by 3 days instead of driving all the way back to Denver and exchange cars. They said no that we would have to come in. So we drove the 2 hrs back to Denver. I went to the return desk, and after explaining our situation, she said I needed to go to the pickup line....which once again was very long and none of the kiosk were working for at least 30 minutes. When I finally got to the agent, she said we could have just gone to the return desk. ARGHhh. We again asked if we could just keep the same car and she said we could not because it needed an oil change.
 
She told us where to park it, to leave the keys in it  and gave us the slip to get our next vehicle. We did not pay for the fill up on this one as we didn't plan on driving it much and thought we could fill up on the way to the airport. So when we were driving back to turn it in, we filled up in Frisco as we thought it would be much cheaper than at the airport and we could just pay to top it off there. When we got to the airport we went to the gas station at the airport and filled it up and then returned it. And we thought that was it.
Well we were wrong. We had been home over a week and started recieving automated calls telling us that the first car had not been returned and gave us a number to call. But when we tried to call the number, it said they were closed on the weekends...even though that is when they called us. We recieved 4 more of the same phone calls before we could call back on the first day they were open after Memorial Day. The guy was very nice and said if he had any problems he would call us back. We never heard from him, but yet recieved 2 more calls from the automated people!!!!
Then last Friday we get a letter in the mail stating that "although the car registered "Full" on our arrival, when it was serviced for the next renter they had to put in 15.69 gallons of gas and had charged our credit card $153.45!!!!
We were appalled. We have reciepts from when we filled it up in Frisco as well as when we topped it off at the Denver airport. We have disputed the charge with our credit card company and will send our proof to Hertz and hopefully get a refund on those charges. While we realize that it may have taken 1/4 or 1/2 gallon to bring it up to above full as we know that the needle will go beyond "full", it did NOT IN ANY WAY TAKE 15.69 gallons. And to charge us $153.45 is absurd. I will keep you posted on how they respond.
 
I will say this is the worst rental car experience we have ever had and we vacation every 6 months.