Hi there,Welcome at the Spotify Community!
I'm sorry for replying in English, but most of the users understand English.
If I've translated everything correctly, you've had premium before which worked properly. Now you can't download most of your songs for offline use.
Have you already to tried to logout and login afterwards? Sometimes something simple as this already fixes the problem.
Also, do you have enough free disk space left on your iOS device?
And, how much songs do you have? Spotify has an limit of 3,333 songs which might be saved for offline use.