So you need to have email confirmation about the offer letter along with salary break up and email acceptance should be made from both side, and also you need to have the email where the future employer is asking you to resign from your existing job.
Try withdrawing your resignation from your existing employer before you proceed with any legal steps,
What is current status with your company ??
Have you been given your F&F settlements ??
It was naive of you to resign before getting a written offer in hand.
If there is still a chance; request for withdrawal of your resignation and continue your employment with your company.