But the email said I had been downgraded which was 100% incorrect

If they want to audit my account they can but surely they could have sent an email saying something like 'we are deligeted to confirm your diamond membership runs until the end of 2023' rather than one that gives an incorrect status.

As I wrote I had achieved Spire / Diamond by the end of March last year way before any stay X nights and get Plat and Y for Diamond offers or the Amazon corporate offer was released into the wild.

That said it looks like thi syear I will need either another double qualifying points or a stay Y nights offers!