Promotion during Maternity Leave regarding

Presently i am working as Accountant in a central government department where i joined as Accountant (2800 Grade pay) on august 29, 2012. i was promoted from Accountant to sr. Accountant (4200 gradepay) and the order to this effect was issued on April 01, 2016. when i was promoted by my office, i was on maternity leave w.e.f. March , 2016 and i was blessed with baby boy. My office seniors said that as I am on maternity currently, I will not get benefits of promotion wef order issue date. As per them, once I will join the office my promotion benefits will be effective for that date only. i understand that maternity leave is a kind of leave which contains all sorts of benefits to the women employee in the manner as it should be for the person who is in continuity of the service. in view of the above, i would request you to kindly provide me copy of the related rules, regulations and oms for central government employees, so that i may pursue my office to get the promotion benefits and other dues with the due date i.e. April 01, 2016 accordingly .