Visiting India - OCI stamp not in new passport

[maharathi]

I landed in Chennai today with my US passport and OCI card. My passport did not have the OCI stamp as it was in my old one and I thought my OCI card should be enough to go through immigration. I was stopped and told that I need to pay Rs.2,020 to get 72 hrs permission to stay. I was told to get an 'exit certificate' from a police station so I can show it when I leave the country. I am staying only for 4 days (96 hrs), but not sure what I need to do to get this 'exit certificate'. I coudn't get much information from the Bureau of Immigration.

Any help at the earliest will be much appreciated.

Thanks