Before proceeding with everything, let me ask you a few questions. Have you spoken to the HR department of your company? What is the reason for withholding your FFS (Final Settlement)? Was the separation from your previous company normal, or did it have some negative connotations? Were you asked to resign? Do you have proof of handing over and taking charge? Have you obtained clearance from all departments?
When you contact HR, be polite and consider recording your call as evidence, but do not disclose that you are recording the conversation.
All the best!
Regards,
Dinesh V Divekar