You showed them the check-in paperwork and they accused you of having forged it? I wouldn’t let this go - I’d definitely do a chargeback if you don’t get a resolution from them today. $70 for 10 gallons of fuel is highway robbery, especially if the vehicle was within a gallon of full. (It's not as if they can’t verify the vehicle was refueled without a receipt from you - they know how far it was from full when they refueled it, if they did.)