You cannot convert torrent to mp3, or any other file format for that matter. It is just link, that points a special Bittorrent program where it can download the files listed in the link. The only thing you can do is to open the .torrent file in one of the many download clients and download the MP3 file, but no torrent to mp3 conversion is possible.
In a word, direct torrent to mp3 conversion is not possible.
So don't expect any so-called torrent to mp3 converter or torrent to mp3 free online conversion tool available.