Charge for fuel when car returned with a full tank

Car returned to Inverness Airport at about 1100 on 27 July. The gauge indicated full on arrival( more full than when I took it out). I had filled up on the outskirts of Inverness en route to the airport. As a modern diesel,it certainly didnt't use 8 litres (1.75 gallons) in the distance from there to the airport. Which is what you have charged me for, £12.48!!

Please explain this matter, asap.

P Gordon  (invoice No.100401594016 dd.27. 7. 09)