I used an app to download a MP3 file from internet, i am able to play the file from within the app however am unable to access or play the file from Xbox music app.
Windows phone 8 Nokia lumia 720 Application : Big file downloader
I tried connecting the phone to PC and access the data still it doesn't show up anywhere in the memory.
Big File Downloader is a Windows Phone 7 app, which means it will also run on Windows Phone 8. The problems is that WP7 apps cannot save songs/tracks to the Music+Videos hub, but WP8 apps can.
Also, when an app saves data like a photo, video or song - it cannot be seen by other apps or if you connect your phone to a PC or Mac. Basically, there is no way to get at the song unless there is some sort of export option via email, SkyDrive, Dropbox, etc.
You could contact the developer and ask for an update the app to include such features or provided a native WP8 version, which would alleviate the problem.
Each application gets its own private data store - you would need the application to support saving/exporting to the music library - there is no general purpose file system visible between applications other than the built in libraries.
At the time of writing, "Integration with central Audio/Video hub" is listed as a future enhancement, so it may come later.
