Did you land at any of these?
Berlin (Tegel, Tempelhof,
Schönefeld), Bremen, Dresden, Düsseldorf, Erfurt, Frankfurt,
Hamburg, Hannover, Köln/Bonn, Leipzig, München, Münster-
Osnabrück, Nürnberg, Saarbrücken, and Stuttgart
If so, then check the receipt carefully, because DFS charge Terminal Fees for approaching the airport. I got caught by Nürnberg once. No big deal, but paid landing fee to airport, but DFS billed me separately for the use of ATC facilities to land there. Can't remember how much I paid now.