Refueling charges on full tank. **** ?

Rented a full sized car. First car was in poor condition lots of damage and not cleaned. They react well to me pointing it out and immediately replaced the car. Good reaction after a poor start. After I returned the vehicle I was surprised to see additional charges for refueling the car. I returned it after filling up 400m from the return point. They claim that they can fill a further 10-15 litres on all cars after its full so I am liable for almost 11 litres. I asked the attendant to fill it up so not sure how this is possible. My query was closed without contacting me other than an email to say its closed. No discussion. This has all the hallmarks of a ****. Do not recommend using a company with hidden charges or dishonest practices