Property without oc and cc

We saw a building with 6 apartments (fully constructed) in Bangalore Koramangala and planned to buy it. We asked multiple times to the seller for the documentation and he and his staff confirmed that their banker is SBI and they will arrange for loans immediately without documents bank won't disburse the loan. We paid them the amount of almost 15 lacs (20%) of the property and applied for the loan. We insisted on HDFC due to their quick processes and HDFC gave me an in-principle Sanction. I learned from my RM that the seller side is delaying with documents and the project is not approved by HDFC. After a month of continuous follow-up, the staff from the builder called and said SBI approved the project and it will be possible to get a loan from SBI easily. In the meantime when we asked about the Occupancy Certificate and Completion Certificate, they said they have applied for CC And OC is not needed in Bangalore. SBI RM also confirmed that they can disburse the loan without these certificates. But followed by a month, SBI RM confirmed that there are deviations in the building so they cannot provide the loan. I approached the seller for a refund of money and to cancel the sale agreement (just in stamp paper not registered yet), The staff said that there will be cancellation charges and will not refund me till they get another buyer for the flat. I have so much emotional damage, money spent for pooja, etc on their fake promised, and vacated my rental house based on their promise of possession. What right do i have as a buyer here and how can I get a refund of 15 lacs?