Hi
1) It is ridiculous on part of SBI to ask for OC for a 7 year old flat and that too when you have OC from gram panchayat.
2) Since the flat is a 7 year old flat and is a resale, in lieu of OC from town planning authority, you can ask for the following from present owner of the flat
a) Building plan approval issued by gram panchayat.
b) Property tax (up to date) paid by present owner
c) Electricity and water bill in name of present owner.
d) Copy of OC issued by Gram panchayat
and enclose the same along with your loan application to HDFC bank
3) You may go ahead with the purchase of flat, subject to HDFC granting you a long term (7+year) housing loan (not loan against property) for the said flat. In general, if it is a long term loan, housing loan process is very strict and in general, HDFC bank has a good legal and valuation process for vetting of home loan applications
Hope this information is useful.