the building is done well - no other neighbour is having that kind of problem. My bf's uncle who is fixing our bathroom said that the previous guy didn't put this adapter well, that's why we had the leak. He put it well, the other guy did the water pressure test and no leak!
But as I said, the insurance guy has to come and check/do the photos if the insurance may cover it (no single word about the guy who was doing the bathroom - we had no agreement with him, no proof..) - so we say that it has happened itself
(ps. that's what the consultant in the insurance company told me to say)
Now better news: In 3 hours I'm going to Puławy to do the hair cut (I don't know, maybe I will have shorter hair?), do the blood tests (thyroid). On Monday - biopsy.