Education loan- index2 of mortgaging property not available

I am student applying for education loan. For the mortgage I am keeping our residential flat. our flat is part of Co-op society which can be owned by only Pune corporation employee.The flat was purchased in 1993. we have 1-allotment letter from society of flat 2-share certificate from society 3-Receipt of the payment of the money when flat was purchased. 4-property tax receipts 5-MSEB receipts all in the name of my father yet the bank legal advocate is saying the loan cannot be sanctioned. need help