It is true, the written English in the OP's input is not the best, and the OP could have done better if he/she was a real teacher of English, whether native speaker or not. Nothing to do with colour, ethnic origin or whatever.

Apart from that, it is crappy Chinese bosses of filthy training centres taking advantage of paying lower wages to those you have mentioned. If they were genuine, they would pay more and try to get really qualified people, who may expect a better pay. But no, they don't because they even don't know what quality education is.

But that's China!

I don't think we have to go any further than what you quite rightly said, that the OP's English was really very bad; and that's no surprise because English is not his first language. He probably does a very good job within limitations, but those limitations means he should not expect the same money-he can't do the same job. He should study hard and become as good as the rest of us. I don't blame his bosses for paying him what he's worth-not a lot I'd say.