Employer denied experience certificate and salary dues

Even after getting no dues signed by all the stakeholders and approval letter signed by my professor at IIT Delhi for release of my experience certificate, I was refused the aforementioned certificate. My professor sent me an email saying he takes his approval back blackmailing me to remove a publication who was my original work. nnI have sent IIT Delhi a legal notice and even emailed it to all the management but they didn't reply to it. Even sent them an RTI because govt. funds were misappropriated in the project I was working on. Even they have provided false information and suppressed details in the response to RTII want to initiate an action against them but also don't want to spend too much money as I am not working right now.