If your journey is of a private nature, then, in the case of flight disputes, you have the right to contact Schlichtung Reise & Verkehr, Germany’s independent arbitration board for travel and transport that oversees all carriers.
You may do so if you have concerns relating to
The postal address is:
Schlichtung Reise & Verkehr
Fasanenstraße 81
10623 Berlin
The European Commission also provides a platform for Online Dispute Resolution (ODR):