Downloaded song keep getting deleted (Iphone)

[musiccornercv]

A few days ago it was my birthday and I got Spotify Premium from a friend. I loved it. I freed up some space on my phone and downloaded about 4GB of my favourite songs. A few days everything was well. But now everytime I restart my Iphone or sometimes completely randomly, Spotify deletes all my downloaded songs. Now I do have a slightly unstable internet connection so it takes forever to download them. Over and over and over again. Spotify also appears to think that when I switch off 'Download' I actually mean 'Wipe everything you've ever downloaded'. 

In short: My downloaded songs keep getting wiped for seemingly no particular reason.

Steps to reproduce the issue:

1. First I downloaded all my songs.
2. Then I switched off my phone.
3. My songs were still there.
4. I downloaded some more songs over the course of a few days.
5. Then I switched off my phone again.
6. All my downloads were wiped.
7. I redownloaded all my songs.
8. Spotify glitched. (Or at least, the song lenth was reduced to "--:--" and then the app stopped completely, this has happened about 3 times now?).
9. I restarted the app.
10. Songs were still there.
11. I played a few songs.
12. All downloads were wiped.
13. I redownloaded the songs.
14. I listened to them for a while.
15. I connected to the internet.
16. All downloads were wiped yet again.
17. I redownloaded the songs.
18. Everything seemed well.
19. I switched off downloads for a moment.
20. ALL DOWNLOADS WERE WIPED AGAIN
21. I downloaded them once more.
22. I was very cautious this time not to do anything that might wipe them.
23. They got wiped when my app restarted.
24. I added a few songs on my computer.
25. I downloaded those and guess what happened next.
26. Etc.

Steps I’ve tried already:

I have tried switching internet connections, removed then reinstalled Spotify, I have tried switching downloads on and off and on again, I checked my settings, read as many threads on similair issues as I could muster, I have asked my Spotify nicely and almost thrown a hissy fit. I was so happy when I got Premium! I'm positively annoyed now. If this is the standard quality of Premium I will certainly not get a subscribtion. 

Device and operating system: Iphone 5 on IOS 9.0

Subscribtion: Spotify Premium

Version of Spotify: The very latest since I reinstalled