Annual performance bonus

Hi,
I am working in genpact from past 7 years.
Company will make annual bonus related to Jan to Dec in next year March month salary.
For eg 2020 bonus will be paid in March 2021 salary.

However, I have resigned in the month of March before the bonus got credited to my account.

I got the bonus letter also but they are stopping my bonus payment.

Policy says : Emoyee should not be serving notice period at the time of bonus payout.

I am serving notice period.
But I feel this is injustice from employee part as the bonus earned for the last year performance and they are not paying it after allowing the amount and bonus letter just because serving the notice period.

Is there any way that I can get my bonus as it is my earned Money for my last year performance.

Thank you