it sounds to me that you got something wrong. Did you file it correctly by saying you are not a US citizen? I know poland has a tax treaty so you should ask them for the tax to be reduced correctly under Poland tax treaty.
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You should be applying for one of those, let me explain what they do:
- Individual Taxpayer Identification Number (ITIN)
This one is to report taxes only, nothing else.
- Employer Identification Number (EIN)
Is used by business, you may apply for it but you need to do lots of things.
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You want the ITIN if you are not planning on going big, otherwise use EIN if you do plan on making a business.
I do not know what paper you need to apply for, it is different for people who did not visit or never file taxes for US. I highly recommend asking someone who knows more about it than me.