Why is bank delaying final payment despite property registration done?

The bank is holding the final payment to the seller and insisting that the buyer obtain an NOC from the housing society confirming that the buyer agrees to abide by the bank loan terms. The bank had earlier instructed us to complete the property registration, which we did, but now they are asking for additional documents like the NOC and society share certificate. Since the seller hasn’t received full payment, how can the buyer arrange these documents, especially as the seller hasn’t handed over the property keys yet? Please guide on what should be done in this case.