Notwithstanding the above, if you want to draft your own claim and represent yourself, it should cost much money, and would at least get their attention.
Might come to that, one slight snag is that the aircraft is based in the UK, and I'm resident in Ireland, so even filing the papers is not that simple, and I fear that the operator is relying on that.
One of these days I shall be visiting family in that part of the world, so may well call on them without warning, and make it clear I'm not leaving without a solution.
Sore point all the way round, there's a lot more to this than just the headset, but this thread is not the place for it.
Thanks for the ideas.
Cheers