No Full & Final Settlement after 3 months of resignation

I was working with a company which is a part of Group of Companies. I worked there for 4.5 years in IT Department & my reporting was directly to the Director of the company, initially everything was good but after 3 years management started delay in salary by saying they are under a loss. Delay in salary gradually increased to 3 months and in the mean time many of the staff may asked to leave by the management or they resigned by their own but Full & Final settlement is not done for them as well. on Mid-Sept 2017, Director of the company asked me to resign with an verbal assurance that they will settle all my dues (pending salaries from July to Sep 17 + Earned Leaves and unpaid bonus) within 2 months. But even after 3 months nothing has been done. I have sent several mails to the Director, sent whatsapp messages and calls but all goes in vein. Kindly suggest if a company is under a huge loss can delay or write off pending dues of employees? or can I send a legal notice to recover my money from the company?