Basically I've had issues within the past 2 days. I've been a premium user for around 4 months and used spotify on my mac and 2 iPhones. I've only downloaded around 1000 songs as well. And now for some reason, even after the devices have been reset by a moderator, it will download 18 tracks of the playlists of my choice and nothing more.
Spotify recommends 1GB of free space before downloading any music on iphone and the red exclamation mark usually indicates that there is insufficient storage. Pleasee try reinstalling spotify to clear the cache and see if downloading works.