Legal remedy as police not filing FIR for a case of forgery

I had given a written complaint against my father with proof that 23 years ago he had forged my mother's signature and mortgaged my mother's property and taken a bank loan, due to which under stress my mother died. Now i have given proof of forgery - Signature verification document from an institute. But the police has not filed an FIR against my father, who should i connect with if they are not filing an FIR, because if he has done crime he must be punished.Who should i meet to get the FIR done ?