Insane denied boarding story - what now?

Currently in Amman, Jordan with an Irish passport. Husband holds Indian passport, recently naturalised, waiting for his Irish passport so still holds his Irish/EU residency permit and carries his naturalisation certificate when travelling. No issues transiting from U.K. to Amman from Ireland, even stayed a few days in U.K.

About to head on a flight back to London, with a same day connection back home to Ireland using Wizz then Ryanair. Ground staff of Wizz refuses to issue his boarding pass stating he needs a transit visa even though the government website AND U.K. visa centre clearly said that he does not require a transit visa landside if he’s 1) transiting to Ireland with an onward flight ticket and 2) holds a residency permit. We printed and checked this pre arrival. We’ve also done this before from other countries and even showed the stamps! And showed the gov U.K. website which clearly shows this is allowed. Nope, 2 hours of arguing and the incompetent agent stating firstly 1) landside transit means you come by car 😭 and 2) onward ticket means the ticket has to be on one single booking and cannot be separately booked tickets.

Ground staff sends an email to U.K. immigration, who advises 30 minutes after the flight has left that we shouldn’t have been denied boarding. Ground staff admits fault, but refuses to provide us with documentation stating they wrongly denied boarding. We get a new ticket home via Vienna for > €800 for both of us. Wizz says they won’t compensate without a denied boarding form, which ground staff won’t give.

Have logged claims anyway. Any other suggestions?