Employment law issues with a language center in Hanoi

It was a referral, because that other center couldn't find someone with my mother tongue. Later, it dawned upon me that they would be getting a cut for this service as my agent

They had Vietnamese teachers who earned ~25% of what my contract stipulates. After a few weeks, the manager might have buyer's remorse? She became hostile, pestered me with lesson plan demands and came to observe classes without understanding the language. But that's life.

Then she ordered me into the office on a Saturday morning (I had weekends off). Surprise! She fired me.

But then the following e-mail was sent:

After X weeks you teach at my center, I have asked  my friend - a lawyer about your teaching at my centre and he told me as followings:

1. Firstly, about the Agreement I signed with you - it is not valid. According to Vietnamese law, every document made in Vietnam must be both in Vietnamese and other language (if any) but in this case, I signed with you one that is made in English so it does not come in force. In addition, the Agreement I signed must be stamped with a legal entity but in this case, it is not.

2. About your CV you sent me last time, you mentioned the work permit but in fact it in only a TOEIC certificate and with this Certificate you can not teach at my centre
because you violates Vietnamese law.

So now, if you want to continue to teach at my centre, you should submit me the original of your work permit in Vietnam and other documents that show you live and work in Vietnam legally then we will signed a contract according to Vietnamese law.

​We will meet at 9:00 on Monday morning, date June 29, 2015. If you do not come and submit me documents as I mention above then I will stop your teaching at my centre.
About your salary of a X-week teaching trial at my centre ($ XXXX), ​you can come and receive at my centre from June 29, 2015 to July 1, 2015. If you do not come within this duration, then you have to wait to the duration of next month. After two months since  June 29, 2015 if you do not come I have my own right to decide about your salary.
...

Please re-read the last sentence. I never got 1 Dong.

The Business Visa for 6 months cost me ~ $ 500. I never had a WP in Vietnam Claiming to have one would be silly, JMHO. And I doubt that a WP can be "transferred" across provinces, even if it was permitted to change employers without changing the WP (which I doubt)

Neat, isn't it? Now it will be up to the manager whether she will pay me at all"!?

She had used some Chinese contract in English and as a foreigner who neither speaks Vietnamese not knows the local rules, I don't feel guilty about her business practices.

Any comments?

I'd like to get paid and move on. As rewarding such behavior would cause trouble for future employees.