Query regarding gratuity claim

Sir/Maam, I have a few queries regarding my gratuity claim.I had resigned from Mother Mary's School,Mayur Vihar,Delhi-91 on October 2016 after working for 6 years.I applied for gratuity on 6th March,2018 using Form I through registered post.On inquiry,the school authorities acknowledged the receipt of my application on 6th March,2018 and informed me that the accounts department will revert back within 30 days as per the gratuity rules.However,the 30 day period is due to expire tomorrow and I am yet to receive any communication from the schools end. Under the present circumstances,kindly guide me with the my next step. 1.Should a complaint be registered with the concerned controlling authority after 30 days and if so, kindly inform me about the concerned controlling authority for schools in East Delhi? OR 2.Should a reminder be given to the school authorities with a warning that a formal complaint would be lodged with the concerned controlling authority? OR 3.Should I send a legal notice. Your advice would be highly appreciated. Regards, Nibedita