Probably not best to bring up the 'extraordinary circumstances' clause since Jet2 recently lost their appeal for using that excuse.
Yes they did, but are still refusing to pay up whilst a case relating to another airline, Van der Lans v KLM, goes before the European Court, in the slim hope that they can piggyback if the judgement is made in favour of the airline and not pay out.
A test case is due in Liverpool County Court, Allen V Jet2.com, before the end of the month to see if this further refusal to pay has any legal standing.