Harry: I think I know better if Norway accept dual citizenship or not and they don't.
OK, read it on the Norwegian government's website yourself:
You can have dual citizenship if
If one of your parents is Norwegian, you probably automatically became a Norwegian citizen when you were born. If your other parent's home country has the same rule, you will also be given that country's citizenship and you will thus have dual citizenship.
A person can't just give up Polish citizenship. A person can only apply to President of Poland for permission to renounce citizenship; no presidential permission = no renunciation. newyork.mfa.gov.pl/en/consular_information/polish_citizenship/renunciation_polishconsulate/
When I contacted immigration ... they still told me that I'll lose my Norwegian citizenship.
Refer them to Chapter two, Article 14 of the 2 April 2009 law on Polish Citizenship:
Article 14. The child shall acquire Polish citizenship at birth when:
1) at least one of the parents has Polish citizenship;
Also refer them to Article Article. 6. 1. of the Act on Polish citizenship dated 15 February 1962, as that is the one which applied when you were born:
The child of parents, one of whom is a Polish citizen and the other a citizen of another state, acquires Polish citizenship by birth.
As I said I'll call the embassy in Oslo tomorrow and talk to them.
You'll want the consulate, not the embassy. And they can only tell you what Polish law says, not what Norwegian law says.