These is just propaganda for internal use before upcoming elections. The target demographic group for the extreme right wing party are old people who still live on WWII stories told by their parents and family. Fostering anti-German sentiments is a big part of their propaganda. Most younger Poles don't take it seriously and are not happy about damaging relations with the neighbor. Unfortunately the opposition is split so the ruling party is the largest with less than 30 percent of the vote.

Poland got screwed with the deal during Yalta conference but it's done. The Soviet Union, the occupier back then, represented the interests of Poland in the conference.