David WE Roberts wrote:

it looks as though my main hope of
getting my money back is via the Amazon dispute process.
So has anyone used this successfully?

Yes, ordered some old-hat RAM from a German seller via Amazon, it was
down as 3 weeks delivery which I could easily live with, after 6 weeks I
remembered it should have been delivered by now, asked supplier who said
sorry and it would be on its way, after 9 weeks still nothing, I warned
them I'd have to use Amazons dispute resolution if it didn't arrive by
12 weeks, on the final day I filed a non-delivery report, the seller
agreed and I got an offer of the dosh back, or a credit note for the
dosh+10% the same day.

A bit odd, but it worked out OK and the RAM was by that time available
even cheaper from someone else.