The NEB 'responsible' for your flight is the office in the country you were departing from however they have no jurisdiction over FR to compel them to supply information as to the reason for your cancellation/delay. Legally FR can refuse to provide and whilst the NEB may agree with your position (due to lack of FR response) again their agreement will not stand for anything should the matter go to court.
With regard to any threat or action you wish to legally take against FR you can either use the EU Court procedure which can be submitted via a UK Court (Sheffield appears the best versed) or indeed you can use the Dublin Court but you cannot use MCOL (internet - money claim on line) or form N1 (standard form for 'small claims') however I would expect FR to defend any claim of the type you mention due to the impending strike. Accept the strike did not occur on the day in question however a judge may regard the impending strike as good reason to cancel a flight the previous day.