I've been in a similar situation to you in China not so long ago. If you don't mind, I'll give you some advice concerning how to proceed in the near future.

Get out as soon as you can. In your case, that will probably require you to take another teaching post very soon, and leave there with your 5200 RMB, to cut your losses while leaving your school with egg on its face, ie one foreign teacher short at very short notice. Remember that if you walk between paydays, you'll have done your school a big favor by working for free, as the salary owed to you at that time will be withheld! Best to walk as soon as you've been paid the previous month's salary. That means you'll only teach 3 days for free. Or you can always claim a bad back, and go sick till you walk! Just the kind of deception your crumby school deserves!
Do not name amd shame that school till you've left and are well clear. But if you can't get another job fast, keep your mouth shut while you complete your contract.
If you tell others there about your having been cheated out of a month's salary, you won't get support. On the contrary, you'll be ostracised and deemed a troublemaker! Chinese stick together, even when they're in the wrong! I suspect you already know that.
Don't report the school to Beijing for contract breach. If you do so, the word will get back to your bosses at your school very quickly, and you'll be persona non grata there until your contract is up. It's terrible to be shunned and scowled at, even worse than being a leper, I'd think! Not only that, but the school will try to find fault with your teaching in order to take its revenge.
Finally, I'd say that if you don't have a work visa, you can leave without fear of reprisals. But if you have one, beware of being blacklisted, which will prevent you from teaching in China therafter. Hopefully, you don't have a work visa. I didn't have one when I got out of a crock of s_ _t similar to the one you're in.