Hi @AndyOfEngland2, welcome to the Sonos Community!
I’m sorry to hear that you’re still hearing ads when using a paid Spotify account.
Did you add Spotify to Sonos when you were on the free version, or did you add it when it was paid?
Either way, you’ll want to reauthorize the Spotify service by opening the Sonos app, going to Account → Content Services → Spotify → your Spotify Account → Reauthorize Account. While they may be linked that they show the same playback history, the account type may not be the same between Sonos and Spotify. If reauthorizing doesn’t help, try removing the service instead. The process is the same, where you go to Account → Content Services → Spotify → Remove service. After removing it, add Spotify back to your system and test to see if you get ads.
Another test would be to use Spotify Direct Control and stream to your Sonos speakers using the Spotify app. It would be good to know if you still get ads when trying this.
I hope this helps!