Local files won't play on phone but will on PC

[UnknownOrigiinz]

Hi all,

I used to be able to listen to songs from my computer on my phone (iPhone) and on my spotify app in my car, but recently I haven't been able to get it to work. On my phone, it says the music is there in a playlist and downloaded (with the green downloaded icon and everything) but when I tap on the song nothing plays. If it comes up on shuffle, it skips the song and goes to a song that isn't a local file. Funnily enough, I can select these local songs from my phone to play on my computer, but when I switch it back to play through my phone the music just stops. 
I've tried importing all the music into a seperate playlist and adding the songs, but still nothing. Is there anything else that I can do?