Hertz Car Rental Snuck in an upgrade after I clearly had prepaid for my vehicle in Los Angeles California

At Hertz Los Angeles Airport location: A customer service rep snuck in an upgrade on a vehicle that I did not order. I had prepaid for my vehicle and SAID that I did not want to pay anything additional. They tricked me into an upgrade that matched (almost exactly) the amount that I prepaid.

I did not realize it at the time  that this was additional (in the middle of the night at a kiosk at LAX with a customer service rep on a phone- not a live person) When I saw the charge after I returned home and called in I was told "You signed the contract- there's nothing we can do" but it's so obvious that the customer service rep was taking advantage of me to make their commission!!!  Hertz ripped me off.

They offered to give me back 10%. I said yes- please give it back- but not that I was not wanting the rest back. So next they tell me, "You agreed to the refund that customer service offered you" as if that meant I would not be receiving anything else. I did agree to the partial refund but not that I didn't want the rest too! 

Makes me wonder how often the car rental representatives put you into upgrades that you don't want- and people don't complain so they get to keep doing it!