Hello @DrGiles, thank you for supporting us!
It seems your subscription isn't linked to your Windy account yet, it might not be active yet. I would recommend following the steps in this manual on the device you bought Windy Premium: https://community.windy.com/topic/11832/what-to-do-if-you-can-t-access-your-windy-premium-features.
Once it is done, all you need to do is to log in with your Windy account on the website and Premium will be available to you.
You can also tell it is linked to your Windy account by the Premium batch, which will appear here on forum, next to your username on your posts.
I would also recommend checking if you are subscribed to our application, we are Windy.com, red and white logo, not Windy.app, blue and white logo.