Doesn't using Spotify on Sonos require a premium account?

If not, I'm not sure why I'm paying any more.

That's really the only thing I wonder too now, else I will cancel directly too

As far as I know you can't listen to spotify using 3rd party clients (like the Sonos).

You can, but it does indeed look like you still need Spotify Premium. https://www.spotify.com/us/sonos/

From the article: "We have removed these caps completely across all platforms"