Dear Himanshu Sharma,
The bonus mentioned in the offer letter is not in absolute terms but only an approximate amount. Whether it is statutory bonus or otherwise, its computation and payment is based on the period of any stretch of consecutive12 months depending upon the Accounting Year adopted by the organization.
Your post indicates that the Accounting Year adopted is the Financial Year comprising of the 12 month period commencing from April,1 and ending with March,31 every year respectively. Admittedly, you've joined in February,2017. When the accounts of the Company are balanced for the financial year 2016-'17, you will get your bonus proportionately for the period of your service in the FY i.e for the months of February and March.2017 only. Therefore, what your Management says is correct in so far as your eligibility for bonus for 2016-17 is concerned.
Regarding the amount of bonus you are entitled to for the period, it depends upon the fact what mentioned is whether the statutory bonus or otherwise and the componential structure of your salary as well.