Oral Partition Legality

Three persons A, B and C bought a piece of land in 1960 in Delhi. In 1974, they had a oral partition of land and B and C sold their respective share of land. In 2018, A sold his share of property to a builder D and D constructed a four storey building to sell individual floors. I bought a floor in the property from D and applied for a home loan. Now the legal department of bank says that oral partition is unacceptable and I need to provide a registered partition deed executed between A, B, and C and also furnish a Sub division letter (even builder D doesn't know what this document is for). Could you please help how to deal with this situation?