I would like to make a complain about the theft to the police, is it possible now? How can I do it?
Are you sure it was stolen and you didn't lose it? If it was stolen, then report it to the police - here's some info on what you need in case of a stolen phone:
nowydworgdanski.policja.gov.pl/pm9/porady/56598,Twoacutej-telefon-zostal-skradziony.html
Basic info:
lublin.policja.gov.pl/llu/prewencja/for-foreigners/64546,How-to-officially-notify-the-Police-about-an-offence.html?sid=7dc1bce13bed7a7e6f4ceff3bd055556
Btw, obviously, it's always the best to report the crime as soon as possible.