Unknown — People posing as Police Cops

My wife received a call on the 24th Nov'09 eve from mob no [protected] posing as Ast Comm Police, Chennai and trying to harass claiming there is a warrant against some person & that my wife had contacted that person.
The call was threatinging in nature & the person said he would come to our place & had our address to which he was asked to speak to me but is not answering the call now. We are mentally agonised & would request if someone could investigate. Thanx, Aman