Megha 18 January 2022
You may get an affidavit executed in through a First Class Magistrating giving your father's name both with and without the middle name and state that both the names belong to the same person.
Upon receipt of the notarised affidavit, please have the same published in a national and vernacular newspaper. This should be sufficient proof.
Thereupon, you can also attest the affidavit in all your future correspondences requiring your father's name.