Well, having reread your post, I realize that you've already left the school, so that changes things a little. I would still advise seeing a lawyer, but now of course you'll have to make it clear that you were forced out by their unwillingness to compromise. Essentially, the lawyer will be representing you so that you can smooth things out with the PSB in terms of getting a new visa. It will be helpful if you have a letter of intent to hire from another school. Of course they will have to add the caveat that they will employ you as soon as this other matter is taken care of. Since they are well aware that a multitude of employers in China are shady characters, that shouldn't be a problem, but this time make sure you're working for a legitimate school, be it public or private. Give them lots of face by making them see how much you will value their advice and help. Make them see clearly that you have no agenda for being here other than being the best teacher you can possibly be, and that your real goal is to help the young people of China realize their dreams.

Above all, keep smiling.