A policeman beat me unfairly during a traffic stop. What should I do?

I was riding my bike when a policeman, without any barricade on the road, stopped me and took away my bike key. He asked me to move my bike to the side, so I did. Then a shopkeeper asked me to park it elsewhere as it was disturbing his customers. I requested the policeman to return my key so I could move the bike, but he told me to move it without the key. When I requested again, he beat me with a stick 5–6 times.