First and foremost raise the issue by means of an email/letter to the HR asking for settlement of your full and final payment , relieving letter and other formalities. You cannot go for legal action without having any basis in any issue. Send couple of reminders, if required and be very polite and diplomatic in your correspondence but put forth all the relevant facts in your email. Give them sufficient time before you resort to any legal action.
Thanks and Regards
6th December 2018 From India, Hyderabad