A missing song (Tiny spoilers)

When section7 gets destroyd a type of weird music plays with somone singing it's not in any of the play lists though why?

That's just some classical music the President is listening to, more background noise than an actual track in the game.

That musical score is "The Creation", written by a classical music composer called Haydn. It's actually a short piece of the song, and it isn't composed by Nobuo Uematsu, so that's probably why it wasn't included in the soundtrack. Another track that was left out of the OST was the song which plays during the FMV when (SPOILER)Cloud travels through his mind to find Sephiroth for the last time, just before Cloud Omnislashes Sephiroth to death. It contains small pieces of Aeris' theme and probably Sephiroth's as well.

I wouldn't call that last one a "track." It seemed more like a dissonant amalgamation of noises relevant to the final showdown, some of which just happen to be musical. It's a cacophony, not a song.