Complex sentence: The Spanish Version of "Oye mi Canto (Hear my Voice)" was used as b-side of the single, the cover of the single is unavailable cause it doesn't sold as a commercial single.
Split into simpler sentences: The Spanish Version of "Oye mi Canto (Hear my Voice)" was used as b-side of the single. The cover of the single is unavailable because it wasn't sold as a commercial single.