Dispute with builder

Builder refused to handover the commercial property (office space) on the date mentioned in agreement between builder and buyer. In one paragraph its mentioned in BBA that on or before 15th of may, 2022 builder will handover the property and buyer will also make payment on or before 15th may, 2022. As builder was not doing anything in the said premises and only few days were left so the buyer confirmed from them before making the payment that you have not even started anything in the unit so how will you transfer the property. Now builder is saying make complete payment then obtain NOC from us then in 90 days we will complete the unit and then make the payment of the stamp duty for registry then take handover. The question is if builder has deemed cc then how can he collect stamp duty and secondly the date of registry is also not clear. In such a situation can the allottee refuse to make the payment to builder and ask for 10% refund. As per agreement if he cancel the unit then he wont receive anything back from builder (10% amount). if buyer claims from rera what are the chances of success.