Thanks for the suggestion to pay by PayPal, that’s the only method I didn’t try. The app seems to be more accurate than the website in terms of showing availability. For me, Livechat worked (sort of) - the agent set up the booking with a live payment link (which crashed as usual at the end of the payment process). They weren’t able to reset this and eventually told me to phone and after complaining about the whole painful process I paid by phone and the tickets were issued. I’m not convinced this sorry tale has a happy ending yet, I can’t see it as even a pending transaction on my credit card account but maybe it will take a few days to go through - I will certainly be keeping a close eye on it