My full and final settlement was not done till now since my last service till 20th Aug-15

I had been appointed as a Sr manager PPIC in the year Apr 2011 and they waited for my resignation till Aug-2015 and during those periods, they asked me to work as per their convenience even whole night without any benefit. Also no increment done since 2012 till 2015. When asked they didn't even care to respond me. The company was treated me as a bonded labours. On 19th Aug-2015 when I put up my resignation for leaving me 20 days after, they immediately terminated me without any reason on 20th Aug-2015. After several follow-ups, they sent me bonding paper written that I have to agree for there Rs.45000/- only with threatened words when I asked the clarification, they don't bother to respond and every year I kept on sending reminder but no response hence I directly wrote to CMD Mrs.Vinita Jain of Biotique and she kept silence since she is the culprits for my settlement. Now, please let me know how to get my full amount of around ₹630000/- including my extra hours working without increament for 4.5 years