Welcome to FT!

What were you told at the airport as reason for the cancellation? Nothing?
The aircraft had arrived from its previous destination, or your flight was cancelled as the inbound flight was cancelled?

Anyway, if indeed caused by ATC restrictions there is no right to comp. under the EU Reg. 261/04 as it is considered outside the control of the airline/extraordinary circumstances. The question is, however, if true that the flight was caused by ATC. I don't know how/where you will find the answer to that Q.