Blackmailing through hacking my personal email id

Hi Sir,

Somebody has came to know Username and Password of my uncle's emial account. Now he has come to know some serious matters in that email and using the same matters to blackmail my uncle. 

How can we react upon him as per cyber law of India? Please provide details Acts of Cyber Law of India to take actions against him. Also how can we initiate to file case against him in the court.

Thanks and Regards.