debited for fuel after filling up the car just before returning

Hi Mr General Manager of Sixt  

I just fill up a satisfaction request , and put my opinion on the service in Sixt.
However , i just check my bank account , and i was surprised to learn that my account was debited of 19,40€ .
This is for the fuel.
But when i brought back the car , i fill it up at the airport and the gage did not change its position.
I have noticed this to the hostess who took back the car , and she mentioned that on Renault and Opel , the gage often did not work , and that she will advise the washing car service to check the fuel content.
Seemingly they base their assomption on the gage dial ,.

The gas was filled up to full , and i even wanted to leave the ticket because of the gage problem and the hostess said no need and that they are familiar with this .

It is not for the amount it represents , but for the fairness.
Being correct and being rewarded with debit , is frustrating.

I hope that you will credit the fuel amount , which will be just the truth.
I keep in touch .

Best regards
Elie HAMON