Bill, as owner of a travel agent business i should mention that the Chargeback route can be fraught with lots of unhelpfulness from your card bank provider and as for ABTA, well, don't hold your breath with them for sure ....... have they ever paid out on anything one wonders !!!!
My earlier thoughts prevail that getting an independent legal Help Line to give up-front thoughts and then to try to get a good legal team to work for you on a " no win no fee " basis could be very useful ........... independent legal travel might take you some years to get a settlement and only then, if in your favour, would they likely settle " Out of Court " maybe the day before the scheduled trial date ...... maybe years ahead of where you are now
The legal line could be quite draining personally ...... so take care eh !
In Equity you are likely due recompense from somewhere ..... just try to de-stress while you're getting your Just Dues ....... plenty of cups of tea might help
Best wishes and lots of Good Luck
Malc