Thanks for this, appreciated.

Yes there were plenty of flights on that route but the only one that would work for me following the schedule change was a Bangkok Airways flight so I booked that, after the assurances from Booking.com that my Air Asia flight would be refunded. This is all a few weeks ago now, the flight was 21/01.

I’ll try again with the G2G T&Cs and see what happens, will report back for the benefit of any others. As much as anything it’s another reminder to me to always book direct with the airline, sounds like this would have been easily resolved if I had.