You can find the decision on the net and show it to your employers.
If that does not work, you need to file an application for gratuity (format given in the act)
If they dont pay it within 30 days, you can approach the labour commissioner in the area with a compliant. He will be bound by law to send a notice and ensure that the company pays you gratuity
Period of gratuity calculation is from the day joined the organisation till the last working day. Many people thinks as the day employee joined and thats wrong
1. Send FORM I to employer within 30 days from last date of work
2. If the employer does not respond file an application under FORM N before the controlling authority under the Payment of Gratuity Act. Ideally FORM N should be filed within 3 months, otherwise the delay has to be condoned by filing another petition/ application for condoning such delay.