Gratuity & Statutory benefit entitlement

I’ve been working for a Global MNC for the last 17 years and during the last 8 years I’ve been working on international assignments in few countries on temporary transfers while retaining my employment with Indian corporations during my temporary transfers while payroll was controlled in India but payment of salary was made in local currency in respective host countries. I resigned from the Indian corporation entity in Feb 2021 to join the International corporation in Feb 2021 as part of my exit and resignation in India corporation eligible for Gratuity for my service for the last 17 years however my employer in India suggest that gratuity would be calculated based on my 9 years old alary drawn in India although I feel it should be based on my last day of employment for Indian corporation and given even while on temporary transfer to the international location I was employed by Indian corporation only and no other employers moreover my payroll was controlled from India although paid out of India in local currency while my posting there. Can you please suggest what is the legal guideline and what action I can take to contest for my statuary Graturity rights as this is my whole life earning and if they used 9-year-old compensation in India it will be significantly lower because 9 years back I was quite junior in my career? Please advise, thanks