I was in the same situation, only Etihad didnt tell me about the cancellation.
We flew outbound from Prague, but only found out at ICN checkin on the way back.
Czech airline ignored complaints, but a lawyers letter forced them to cough up the EU261.
However, since we had to rearrange flights back to Europe on the day, it was very expensive, so I am now pursuing Etihad for a refund of the unused portion of the ticket.
Still waiting for response, as Etihad claimed that Czech did not inform them of the cancellation