Coerced into resigning from job

Hi sir / mam, recently I have been asked to leave the job all of a sudden citing reason of non performance and attitude issue. Not received any thing in written form before this meeting with company GM, VP and HR representative and as per them they have decided to let me go as they are not satisfied with my performance and also received many feedbacks regarding my attitude. I tried to convince them that I am one of the most looked up to person in terms of work but yes those who do not do their work gets a lot of questions from me which they are unable to answer as they are not doing their job responsibly. They asked me to voluntarily resign and leave all the company property like laptop , id card and all and asked me not come from next day. HR said they will be giving me 1 month salary post the completion of notice period i.e. 30 days plus 20-25 days from LWD. I was afraid that if I retaliate there they could charge me with misconduct and deny me any salary of my full and final settlement. Please now advise can I now send legal notice to the company for not giving me any thing in document for any performance issue or behaviour issue and forcing me to quit the job on which my whole family depends. I was working with this company since 2016 and as per the contract letter either party can give 1 month notice or 1 month salary in lieu. Pls advise ASAP.