Hi, and welcome to the community!
Are you sure you're logging into the right account? It's very easy to have both facebook and Spotify details!
If it persists, I suggest you submit an online contact form; and someone at Spotify should be able to fix the premium and get it on your account, and hopefully refund you for any months where you haven't been receiving premium but have been paying.
If you get an automated reply; make sure to reply to it directly (even if it's from a no reply); and it will be sent to the Spotify staff.
This post was by Taylor - I do not work for Spotify! If this solved your issue - Mark it as a solution! If you like my post - Please add Kudos! || Spotify Profile - Taylor | Feel free to PM me - Here ||