Notice Period Change and FNF Calculation

In October'22, the company changed the notice period from 1 month to 2 months to which I never agreed to and never given any consent verbally or written. I resigned in December'22 and I served 1 month and 16 days on the request of the management to make the new joiner learn the knowhow of the work. Now, I have received the FNF as per 2 months notice period and they have deducted the remaining recovery apart from what I served as notice. So, I have 2 questions. 1) Can the company enforce the 2 months notice without my consent? 2) What is the term "month" is considered as, is it 30 days or 31 days? The company has taken the calculation in FNF as 31 days X 2 (Months). 3) While sending legal notice to the company, how much amount should I claim as to "mental harassment" as I am the only bread earner for the family and I have not been given salary for 2 and half months and when they did give, they have deducted much more than they should have. And still they are not agreeing to process as per the original agreement that I have signed with the company. Appreciate your quick help.