GATEWAY TRUCKS & STORAGE

The business was closed when we arrived soon before closing time to drop off a 1-way U-Haul truck rental. I called the number of the business and was told to leave the truck on the street and put the keys in the drop box. The next day the business called my cell phone and left a message saying that the gas left in the tank was below the required 1/4-full and we could come put more gas in the truck. I was in meetings all day and didn't get the message until evening. When I called them the next day, they said that they had charged us $40 to put more gas in the truck. When I received the receipt via email, there was a red mark at 1/8th on the gas gauge drawing and the charge was $48, including $18 for gas. 
We had put gas in the truck right before returning it and had put in 4 gallons to bring the gas gauge from 1/8th to over 1/4 full.  Our conclusions are that one of the following happened: (a) they read the gas gauge wrong, mistaking the tick mark at 1/8 for the E (which we had initially done while driving the truck), (b) someone siphoned the gas out of the truck while it was sitting on the street, which they claimed was difficult to do, or (c) they lied.