My Mother is 2nd wife of my father and i am working in govt offic

Sir/Madam, I am working in Central Government office, recently i have submitted my dependency certificate to office. Here, i have given the consent of my Mother who is 2nd wife of my Father who is a Ex-Government Servant. However, i was asked to produce income proof of my parents to consider the same. I have produced of income proof of my father [PPO Order] and i have also submitted my mother's annual income certificate issued by thasildar office [15000 only from all sources]. Moreover, my father has never declared my mother name in his office records nor my name in their entire service / records. Presently, i have been separated from my Family and living at a different place in the same city and my mother is still with my father. Now, i have been informed by the Office that, my mother cannot be considered as a dependent person on me and they have given in writing. Please suggest my whether, my mother can be a dependent person under any law or otherwise, how can it be possible.............Please Suggest me