@ Sheroo Pratap,
It has been time and again highlighted in many threads that saying/telling/asking are are all verbal modes of communication and is not on written/irrefutable record, hence difficult to prove and burden of proof may fall upon you.
First of all download the Gratuity Rules of the establishment and Trust T&C etc too.
If these are not kept in your knwoledge domain and access then write that and demand to supply authenticated copy.
The Payment of Gratuity Act 1972, provides for mandatory insurance and establishment can form a trust to manage Gratuity.
You need to confirm whether the Act or some other Gratuity rules applies to the establishment.
As per the Act if the employee has worked for 240/190 days in a year (including off/holidays/approaved leave etc) then employee is eligible for payment of gratuity for that year.
You may reduce your verbal transactions in writing addressed to good offices of appointing authority,MD...........................under proper acknbowedgment................and let your cousnels draft your representations.
You may submit FormI under proepr acknowledgment.