Did you ever find a solution to this problem. I have the same issue, seems Samsung Music ignores Spotify Premium. I haven't found any solution. Did you make any progress.
Hi, Jonty1512. Yes, it's true. I understood, that all downloaded songs in Spotify can only played by Spotify Player. I had the same situation. Despite this I like Spotify app because of it advantages: a huge database of music, multiplatform, excellent system of music selection, connection of social networks, sound quality, cheap paid subscription. Besides, if you have a musical talent and you record covers like me, you can try Spotify promotion.
If you are interested, you can check the link https://spotistar.com .