the police declared it was a civil matter and there was nothing I could do, despite my protest and overwhelming evidence including the call to the police during the beating.
Have you considered going again, with a Polish speaking (and very assertive) friend, or getting legal assistance.
You would certainly be entitled to criminal compensation, however you need to go to a doctor to get proof of injuries, and you must do this right away - it could be too late already. When did it happen?