Non receipt of 3 months salaries

I joined a company on 30/11/2106 and left on 31/3/2017. It was partnership firm . I joined that company in good faith as one of the partner was well known to me hence never asked for appointment letter. I resigned from the my Job through email resignation letter on 20.3.2017 stating my last date on will be 31-March-2017. The company has not given reply my resignation email. I stop going to office from 1st April 2017. The main reason for leaving employment was non payment of salary on irregular basis since I joined the company. The company paid my December 2016 salary on [deleted]. Now, my 3 months salaries are still outstanding from January 2017 to March 2017. I am in continuous follow up with company staff and partners through phone calls, SMS, Whatsup Messages, personal visits to office and partners home. They are not denying for payment but always give promises and date and but not paying outstanding salary dues. They some times reply to my phone calls, SMS and watsup messages but never replied to email. They also do not to reply my phone calls & messages many times. Kindly note that almost more than 3 and half months passed way since I left the job. How can I claim my outstanding due amount. Please suggest remedy. Vikas Pandya.