Wow! That is a really horrific situation!

They are probably keeping your passport to prevent you from leaving.

Go to your embassy, regardless of where it is. If your embassy is in Beijing you need to go there, and you can get there without your passport. They can ensure that you get your passport back immediately and make sure that this doesn't happen to any more teachers.

Why in the world are you staying??? A, stop teaching for them if they are holding your passport. While you are away from your country your passport is your most precious posession. There is no reason whatsoever that they should have had it for more than 2 weeks- I know, I'm an employer here in China and handle our foreign visas.

B, get a hold of your embassy!

C, get a new job!

Good luck!