Why does my saved songs keeps getting deleted and not downloaded?

[Mikamik]

Hello, I just subscribed to spotify premium recently, when I logged in, all of my downloaded songs got deleted, then I saved new songs again but can't download it. 

Then after that,I logged out then logged back in, my old songs were restored and I kept adding more songs.  But when I restarted the app, my old songs got deleted and were replaced by new songs that I recenlty downloaded, also I can't download it again.

How would I fix this problem?