I paid by credit card. But even though the accomplishment - in this case a flight which got cancelled - wasn't fulfilled, the credit card company says they can't proceed with the chargeback. They said they need a confirmation of the airline that says they are willing to refund. Sounds stupid right? Thought the same. But had the same issue with two different airlines, Norwegian International and Vueling.

Maybe I try it again for a third time next week when I'm back to Germany, but I think without any success like before