I got hit with a gas charge for a rental return at JFK last week for a car returned the week before. They said either a receipt or a credit card statement showing the charge would work. I did have the receipt and I took a picture of it and sent it in, but if you have a credit card statement showing the charge you could send that.
They had me email it to
[email protected] along with my rental agreement number. Only 5 hours later they emailed me back stating that the charge would be credited back to me.
I know the gas is the least of your concerns, but this might help.