WMP playlists appear under Spotify

Is there any way to clear cached playlists? I had some hundred playlists in Windows Media Player which my Sonos controller imported perfectly.

Now the problem is that the WMP playlists appear under Spotify playlists and cannot be removed. I've disconnected Windows media servers and removed and re-connected the Spotify account to no avail.

And no - deleting the playlist files didn't solve it either...

Any help is appreciated!