[Mahagunpuram] Penalty on Late Payment

Hello All, I had a question about the Penalty charges to be levied by Mahagun due to late payments by us/ by bank against the Demand Letters sent by Mahagun. As per the contract, any payments delayed by more than 15 days from the date of Demand, attracts a penalty @ 16% p.a. for the number of days of delay. Now, considering that I have never received their demand letters on time (although the date of demand is as per the payment schedule under the Flexi Payment plan) and the subsequent delay by the bank in payment disbursal, I think Mahagun will be charging me a very hefty penalty at the time of possession. Anybody in similar situation or have any idea in this matter?