When should Builder pay the handover delay amount as per the agreement clause

In the purchase agreement of my flat, there was a clause that builder would pay certain penalty if there is delay beyond the grace period. There were delays by the Builder beyond the grace period. He has accepted the delay. Eventually the project completed and Builder sent a note for offer for possession with a final payment schedule and registration. The Delay was 1years beyond the grace period Notice of possession and final payments sent on November 2016. Final payments done per the payment schedule on time and registration was completed on Feb 2017. Till date Builder did not pay out the amount quoting "Possession formalities are not completed" as in final walk through and final letter of possession. my question is this: If the Settlement of Accounts and letter of possession was dated November 2016, and the amount of final payment was settled then, why is the builder holding back money indicating possession formalities are not completed. On one hand, he is using the letter of possession he sent for the cutoff on the delay calculation. On the other hand, for the money he owes, he has not yet given the money inspite of Account having been settled in Feb of 2017. Is he hiding behind this excuse that the formalities of flat handover are not complete hence money is not given? It is almost a year since it is due. For the consideration of the delay amout, he is still using November 2016 (1 year delay) Should the settlement of Accounts and registration be used for the handover of the delay money or settlement of possession formality be used. what is the criteria.