You will have to email proof to them (gas receipt and since you have a pic of the gauge that would help too). It will take them many days to respond. They may issue you a credit after a lot of fussing.

Or, in my case, even though you are right and provided the requested documentation, they will not respond and you will have to dispute it with your credit card company. When you do they immediately put you on the do not rent list.

It's a fairly customer hostile practice that seems to run counter to Ms. Marinello's said strategy.