Spotify will happily unlink your Spotify account from Facebook and has gotten a lot better (and faster) about it in recent days. Several posts on /r/spotify have experience:
https://www.reddit.com/r/spotify/search?q=facebook&restrict_...
https://www.reddit.com/r/spotify/search?q=facebook&restrict_...
Problem is, I use Premium via a voucher from my ISP. My ISP no longer gives these vouchers, and its claimed. So for a new account, I cannot get Premium for "free".
I should feel lucky my ISP hasn't disabled the existing vouchers (the main branch of the ISP did).