If your flight was canceled by the airline, you should first contact the airline and request a refund of the ticket price. Their own cancellation rules are often not permitted, even though they like to refer to them upon a customer complaint.
The Luftfahrt-Bundesamt (LBA) offers a display form of irregularities for compensation and / or care for european passengers in the event of cancellation, delay or denied boarding. Whether or not a dismissal of your complaint by the airline is allowed, must be checked by either a specialist lawyer (for travel law) or the conciliation board for public transport (SOEP). Service Number for the conciliation board for public transport (SOEP): +49 30 - 64 49 93 30 (Mondays - Fridays 11am until 3pm).
Service Number for the conciliation board for public transport (SOEP): +49 30 - 64 49 93 30 (Mondays - Fridays 11am until 3pm).
The SOEP is also responsible for railway, ship and bus transportation and is only responsible for listed members (PDF) , Lufthansa for example is not listed. For package tours the respective tour operators is responsible.
SOEP complaint form for air transportation
SOEP complaint form for transportation by rail (german)
The European member nations have acted to strengthen consumer rights and passed a regulation in 2004 which entitles the passenger to rely on when demanding their rights in case of cancellation or delay of their flights, because only those who know their rights can claim them.
Here you can read the entire text of Regulation (EG) no. 261/2004.