I want to share experience that I had with Eurowings last August and follow up story which ended last week.
I was flying with my wife by Eurowings on route Vienna-Hannover-Ibiza. In the morning we received message that Hannover-Ibiza will be delayed by 4,5 hours, no reason given. After we arrive to Ibiza 4,5 hours later, I contacted Eurowings by their online form, asking for compensation according to EU 261-2004. Automatic answer that I got was that they will answer within 6 weeks. Their whole Board is signed under automatic response
7 weeks passed, no answer. I tried again, same answer. Another 7 weeks passed, I realised this is their tactics. From 120 passengers on board probably only some of us filed complaint, very few probably insisted further.
My next step was contacting LBA (Luftfahrt-Bundesamt), after sending all the documents they contacted Eurowings and finally after 6 months passed 2x400 euros was in my account.
Advice: be persistent, do not give up.