Gratuity Not Paying

Hello sir,
Please tell me how to calculate the interest of gratuity is from date of resignation ? I resigned (illegal erminated) in nov 2012, 5 years 10 months, come to my issue the Datamarshall hr is asking time for process it , almost one month over i think he is making timepass, i can wait more one week then wil send form N to DCL

The service period for calculating gratuity is counted from date of cessation of service to the date of joining.The amount of gratuity is calculated as -Salary ( basic +DA )/26 *15* No of years of service.
Varghese Mathew