Flight delay compensation, all other EU airlines

Hi my family and I where returning from UK to Oslo and the norwegian flight was delayed and then cancelled - I claimed myself for compensation and got this reply
"Unfortunately, Norwegian flight D81640 (EDI-OSL) 22.07.2017 was cancelled. This disruption was caused by extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken*." Disruption type: Cancelled
Reason for disruption: This cancellation was caused by air traffic control restrictions.

So I emailed back and asked for more details i.e. was it due to the original flight arriving late in the first place and not getting a slot etc I wrote I would like further information with respect to "* Flight disruption information Norwegian flight: D81640 (EDI-OSL) 22.07.2017
Disruption type: Cancelled Reason for disruption: This cancellation was caused by air traffic control restrictions.
I wish to know what the ATC restriction where at Madrid airport I think, and was this due to the late arrival of the aircraft at Madrid. It should be noted that culpability for such a cancellation is in large part the airline's, as the airline could have selected another flight to cancel instead of the one the airline selected to cancel. It is the Airline decision to cancel, not the ATC​. So please could I have a detailed account of the reason for cancellation. I.e. timing of flights arriving in Madrid etc .

This is the reply I got : thank you for contacting us again. We regret that you are unhappy with the outcome of your claim.
Whilst we respect your request for further consideration of your claim, there are certain conditions which we must adhere to, in order to ensure that we are providing a fair and equitable service. In accordance with the guidelines outlined in your previous correspondence, unfortunately we are unable reconsider our decision in relation to this matter.
We would kindly advise that the delay was caused by air traffic control restrictions, which is considered as extraordinary circumstance. Unfortunately, we are not able to prepare a more detailed clarification or a report, as information of that kind can only be prepared and sent to National Enforcement Body of the country where disruption occurred.

I want to know if this is true??
thanks
gareth

Thanks Tyzap, I thought as much so from your reply they are obliged to I've a detailed reason why, as the original reason was operational problems!!! So I will keep pushing for the logs etc so we can work out why the ATC restrictions was the excuse.

thanks
gareth

Hi Vauban do you have any suggestions

cheers Vauban