You should be eligible.
However you may go thru appropriate sections on applicability, eligibility and other sections as well of the Act if it is applicable to the establishment or Rules if establishment has its own approved Trust to manage the Gratuity..
The HR of the establishment can confirm the views of the establishment in your case.
Payment of Gratuity Act, 1972
Section: 1
Short title, extent, application and commencement
(3) It shall apply to -
Section: 2
Definitions.
(e) , (s)
Section: 4:Payment of gratuity: (2)
Section: 7
Determination of the amount of gratuity.
(Basic+DA) x15/26xNo. of completed years of services
(part of a year in excess of 6 months is counted as 1 year)
(Basic+DA as per monthly wages last drawn)
If there is no DA then Basic may be taken for calculation.
Although the Formulae of calculation of Gratuity is mentioned establishment is under obligation to supply full amounts received from LIC without keeping any amounts with it, even if amount calculated by the formulae is less than amounts disbursed by LIC………………..
Did the establishment supply any notice before revising the wages and ask for acceptance and did the employees accept in writing?
With the revision the contributions for PF, Gratuity, Bonus may come down and authorities may not agree.
Before contemplating any action to agitate you may visit your lawyer with copies of all relevant documents, understand the merits and proceed under expert advice of your lawyer.