Company not processing my FNF settlement

I was working with a manufacturing company for 3.5 years. I resigned the company 1 year ago. The company was not able to pay our salary from last three months and due to this I left the company with proper approval from my Boss. I did not serve the notice period as I had to join my future company within a week and my present company was unable to pay our salary. In my appointment letter it states that I can either serve the notice period of 3 months or else can pay the basic salary of 3 months. Can I ask them to deduct the notice pay from my FNF settlement? . After too much of harassment, I received the Relieving letter and Experience certificate from them after 8months of leaving but they are delaying my FNF process. They say full and final settlement of previous employees are still pending and they will be considered first. Every time the HR gives some funny reason as if it's my concern that the previous cases are pending. It is now more than a year and they are having same answer . The company is already black listed in matter of paying their employees,contractors,labours and vendors . Can I send a notice to the company legally? Is the company ignoring any law by delaying the FNF settlement? Can Notice period creates any difficulty for me as I haven't served it but managed to get the Relieving and Experience letter? Please note that I have also clear all my dues by taking signature from all departments in the No-due form. Please give me your vital suggestion for which I shall be highly grateful to you.