I just rented a car without fuel tracking and drove 30 miles before noticing the tank was below 5/8. Avis recorded it as full - anything I can do to avoid getting (IMO fraudulently) charged for fuel I didn't use?

My plan is to fill up (miles/app mpg) with a receipt and point to the total mileage difference and ask them how I could possibly have used that much fuel. Does that ever work?

Of course I can't get the office on the phone. Ring.... Ring.... Ring...