Please make sure that your employers ever indeed declare your salary and income tax monthly to the tax bureau. If they never did it before, it theoretically means you have not paid income tax.
If you ever have unpaid income taxes under the condition that your corresponding employer did declare the salary to the tax bureau, the tax bureau will request you to pay it first before they refund taxes to you.
The amount of the refunding money depends on how long you have been working in China, to what extent that the policies apply to you, and how much taxes you have been paying totally. Nobody knows accurately how much the returned money will be until we submit the application to the tax bureau.
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