your first concern should be to take the relieving letter and give it to the new employer.
What is more important to you ? getting Rs. 40,000 from the employer or ensuring your current job is secured by submitting the relevant documents.
So according to me, you need to first accept their pay-cut in the full and final settlement and get your relieving letters. Of if your current employer is understanding enough, tell them that they are not giving the letter because of xyz reasons and that you are willing to share with him the letters to prove your innocence in this matter.
After you have got your relieving letter, etc, if you still feel like taking it up, you can speak to a lawyer.
However, your current employer will not be happy to hear that you are fighting a legal case nor be happy that you will need leave to attend to the court case. And if you are publishing confidential information on social media, your current employer is sure to terminate you as they will not take the risk of having someone like you on their rolls