Can you try going to Edit/Spotify > Preferences > Social Network in the desktop client whilst logged in using your Spotify username and try and disconnect and reconnect to Facebook?It should definitely merge those accounts for you.If not - get in touch with support and they can do it for you!
Hey there you,
Yeah, you! 😁
Welcome - we're glad you joined the Spotify Community!
While you here, let's have a fun game…