Musics unavailable offline after download

[helenatarozzo_]

Hi! I recently made the downlod of circa 300 - maybe more- musics and they were on my cellphone (Android) but now I don't have them (these tracks and others) available/downloaded to listen offline anymore. Everything that was green turned into gray. What could have happend? Is it a matter of the memory of my cellphone? I'm a premium user for more than 2 years... I'll have to download all the stuff again??