I restarted my phone and all of my downloaded music dissapeared

[crnchls]

I currently have no wifi to download songs, so when I went to my cousins I thought it would be a good idea to download some overthere. I downloaded over 3000 tracks and I just restarted my phone only to find out it had all undownloaded! I won't be able to re-download every time I restart my phone, so I would like some help so it will stop doing this.