Initiating legal process against privacy invasion

Hi Sir

I am 34 year old resident of Chennai. I would like to seek your advice with regard to what kind of legal proceedings can initiated against suspected individuals who is keeping me under unauthorised survilance using private detective agents and tracking my movements and using the sourced information to threaten.

I clearly suspect that someone is watching my movements, people who I talk to, my phone, text messages and mails. However I do not have an evidence to prove the same as this suspecious things were came to my notice through reliable source.

I need your guidance on

1. Which legal proceedings can be initiated against the individual (Known individual)
2. How to obtain evidences in such case.
3. are private agents allowed to track movements of individuals on any purpose.
4. Can I complain to police against the specific individual 

Thank you for your guidance