As explained on the Audirvana site, the 3 month offer is not applicable in the UK or US.
Here’s the relevant page:
I was disappointed too (and am also in the UK), but them’s the breaks.
Personally, I am perfectly happy that I signed up to Qobuz and bought the licence for Audirvana. I’m sure that you would be too.
If it’s any consolation, Qobuz have recently reinstated their yearly payment plan, which effectively gives you 12 months for the (monthly) price for 10 months. So if you go for that you could consider it as getting two months free.