1. you can claim damages from the bank by filing a suit. But that is a long procedure and outcome is uncertain
2. you can simply take an affidavit from an authorised person of the bank in which he has to state how the original was lost by the bank and what steps bank took for the same. The FIR and public notice can be attached to this affidavit.
3. also include in that affidavit a declaration by the bank that if they trace the original they will immediately return it to you or to any purchaser to whom the flat may be sold
4. first write a request letter to the bank to provide such an affidavit
5. if bank refuses then you can file a suit as a last resort and claim damages