Very slow downloading speed and no playback

[Daveify]

The downloading speed on my Spotify app is very slow and it stops downloading as soon as my phone screen goes off, even though am still active on spotify.
I also have issues with the playback, whenever am using my phone data or WiFi and try to listen to songs I haven't yet downloaded it stops playing after one song.
I am a Premium user.
I would be very grateful if anyone can give me a useful solution to these problems, I have tried updating my Spotify app couple of times, I have the latest version on the app store but these problems still continue.
I have also tried deleting the app and done a re-download but that didn't help either.
I have good Internet connection always so that can't possibly be an issue.
I will gladly appreciate some useful solutions to these problems, thanks!!