Questions, reporting a listing, working together: write to kontakt@mieszkaniawilanow.pl. You can write in English or in Polish, both are fine.
Reporting a specific listing? Include its address (URL) and a short description of the problem. We usually reply within a few working days.
One more thing worth knowing. The site is run in Polish and only part of it exists in English: the blog, this page, the district guide and the listings browser. The form for posting a listing, the user panel and the legal documents are in Polish only, and the listings themselves are written by their owners in Polish.