My Spotify kept on being connected to an unknown Web player.

[#1]

It just happen and I've never open Spotify on devices other than mine. I've changed both email and Spotify p/w, log out, but it will still suddenly get connected to a Web browser I don't know from where.

[Vasil]

Hey there,

Thanks for reaching out and sorry to see this has happened!

My advice would be for you to change your email password (just in case) and to then go through all of the steps from this article here.
Going through all of these steps should help out in keeping your account secure, but do let us know in case the same behaviour continues to persist.

Tip: Any third party apps can later be re-added if need be.

Fingers crossed all goes well!