Refer to: 7: Determination of the amount of gratuity of Payment of Gratuity Act 1972, and also Sec7A, 7B,8,9..........
The establishment should have supplied notice of Determination of Gratuity to employee, with a copy to Controlling Authority of Gratuity.
The employee can submit FormI preferably by redg. post under proper acknowledgment.
The matter can be put up to Controlling Authority of Gratuity at the location of Redg. of the Company.
Initially you can agitate at your last location in the company, redg. office of the company, location of jurisdictional courts as stated in appointment letter.
You should be entitled to get interest @ 10% p.a for the delayed period.