Indian Consulate Ignoring My OCI

Hope someone can shed some light here. I'm British by birth. Parents came here in 1964. Dad kept Indian citizenship while mum took British. I've given them copies of my passport, my birth certificate (shows place of parents marriage in India), my dad's passport, work letters.
I married an Indian citizen in 1993 and divorced in 2003.
They told me to 'go away' when I went to my vfs appointment. This was in August!! They didn't take a payment from me.
I've emailed the consulate and it seems the issue is not having a copy of my mum's British passport. They called and said 'any passport is ok, even an expired old one'. I don't have access to any of my mum's passports as sibling who has them is uncooperative.
I do, however, have an old passport number and a copy of an Indian bank account which has her photo. The bank account documents her Indian family address. Will this be enough? I've asked them but now they're not responding at all.
If I can prove Indian heritage, why's my mum's passport so important? Anyone else had this issue?

Hi. Oci is only issue to Indian heritage. So they want to see your mum passport as a prove that she is an Indian citizen or British.

They need to ascertain if your mother was ever a citizen of Pakistan or Bangladesh - without the passport as proof they cannot be sure, and so the default position is to deny the OCI.

Do you have any other documents issued by the government of India with her details - or are you able to obtain a her Indian birth certificate?

I am assuming she is no more, if that is the case, you can write a cover letter saying that you have her birth certificate, her death certificate, and her passport is unavailable as she is deceased and you have alternate documents to prove her origin.

A passport number will not suffice. A passport is genuine photo id document that governments accept. Suppose, I were to give you a random number "78hfas886" and say its my passport number would you accept it in lieu of my passport? No, same with the Indian government or any government. They cannot accept a number as per policy.

Your best bet would be to work with your sibling.