My account is playing music from someone else's account

[mondodo]

Hi All.

Hope you can help. 

I had Spotify on during a party and people had access to iot. Since then if I play music using shuffle on any of my playlists after one track music is played from a playlist on someone else's account. None of my playlists are collaborative. 

Any idea what I can do to disconnect or block this person? 

Thanks