The same thing happened to me on September 16th.
My school saw the police at the door and didn’t let them in until they hid 3 of us. They searched the classrooms, then talked to the supervisor. After about 15-20 minutes, she tells us to come out of hiding and go back to the classrooms. We ask if the police have left and she says “No.”
(this was when that little voice in my head said, “Don’t go out there!”)
I should listen to my little voice more often. So we go out, ‘observe’ the class for 4 minutes, and then we are told that the police want to talk to us.
The little voice pops up again, but silly me, I trust my supervisor! We chat it up with the police, then they say they want to check our ID’s at the police station. This was at 5:30PM on a Friday evening.
(fast forward)
It’s 1:30am and after interrogating us, making us wait, and feeding us supper(BK), we write up a statement with the police and are asked to sign the document in Chinese.
For all those people who said, “You shouldn’t have signed!”, I know that I shouldn’t have, but after 8 hours in there with pressure from your boss and the police saying that it’s okay, don’t worry, why don’t you trust us, and them threatening to re-interrogate me and/or deporting me that night, you’d crack too. They also said that at this point, the boss has to pay the fine and that’s it.
So I signed.
Fast forward to November 2nd, I get THE LETTER. We(the 3 of us) are working with the school to see if this can be reversed. I’m not overly optimistic, nor do I trust the school anymore(unless the decision goes our way 
)
I would recommend that you talk to everyone and anyone Taiwanese, because there is the chance that one of them will know “the right person”. We’ve gotten a lot of information this way that we never would have otherwise.
I am expected to leave the country by November 15th if the decision doesn’t go through, so I’m all packed up if the worst happens.
I’ve learned that:
-my boss didn’t pay the fine! I was told that it could have been a reason that we got the letters. She has no intention of paying.
-never leave your hiding spot or run like the wind!
-the police cannot keep you at the police station for more than 3 hours at the police station. Hold out till then and you are free to go; they cannot restrain you.
-some other stuff too, but I just woke up!
I’ll keep you posted, but I’m 99.999% sure that I won’t be here for Christmas… sigh