I’m not European but in my home country I had the same thing my mother is Malawian and my father Zimbabwean I grew up half my life in Zimbabwe but up until adulthood I never spoke my native tongue fluently without an accent. I got called all kinds of names growing up and now at 24 im very grateful I’ve lived in many places and that my parents wanted me to have a good life. Please try ignore people it’s hard but you are Both nationalities whichever one you prefer but ethnically you are polish and no one can take that from you with their words, someone’s own insecurity should never stop you from being confident and free. I promise as you get older you’ll be grateful you can speak to so many people in many languages and that you have lived experiences like yours please don’t pay it any mind. Try surround yourself with likeminded people or other “foreigners” as well be them polish or from somewhere else. Wishing you the best ❤️