No appointment letter given but working at senior position for many years

I have been working for over 3 years in a company (desi) in India, however no formal appointment letter given. But I am on payroll , receiving salary by RTGS every month and also incentive. Now, company wants me to leave. What is the minimum notice period they are required to give and compensation ?
Can I demand bigger notice period/ higher severance package ?

Bigger notice period/severance packages are all matters of negotiation now.
What is the company policy?
Others must have come and gone.
But not a good practice to keep staff without appointment orders.
However since it is a case where even senior staff have worked without appointment orders, now go and speak/write to management seeking clarifications and also put it that suddenly asking employee to quit is a shock and he needs time to get alternate jobs.Negotitate hard to best ability.
Jobs are pretty scarce presently,unless some one has a niche skill.

Thanks. The company apparently has no policy or HR document. This a small size company..which was supposed to become big in a matter of 2-3 years as per vision laid out before me and thus took risk. however, despite repeated reminders did not give appointment letter. I got stuck due to no other suitable job options/ non-selection.

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