Remedy in case of Non payment of Full and Final Settlement

Dear sir/madam, It has been more than 3 months since my last working day in the place of my previous employment. My last working day, as per my resignation letter was 20th June 2017. Despite no mention of notice period in the joining email, I resigned on 23rd May and agreed to serve 27-day notice period. Now, my emoloyer is withholding my salary for the month of May as well as 20 days that I worked in June. What can I do to have them pay the salary? I have a confirmation on the resignation email from the HR id of my emoloyer. I have sent multiple emails asking about the full and final settlement but they haven't replied to the emails until very recently. And now they are citing my performance as the reason for the delay in payment; however, during the time I was working, no communication regarding my performance was made to me, not verbally, not in email. It is only now that I am demanding the full and final settlement, that they have problems with my performance.