Delay in handing over the flat, refusal of paying penalty

I had entered into an agreement to purchase a Flat of 585 sq. ft. on CLP based EMI payment scheme from the builder in Feb 2015 at Ghaziabad. Paid initial amounts through own funds and 30% amount paid by my Banker against my Home Loan. Total 40% amount has been paid. I have not paid any installment till possition. As per the Agreement, the possession of Flat was to be given in 3 Years with +/- 6 months. Further, the agreement mentioned that in case of timely installments have been made & there is a delay in possession, Rs. 5/ sq. ft. per month will be paid to me. I had received the Offer for Possession vide their letter dtd. July 12th, 2019, demanding for the final payments and secure the registry of Flat, which is completely not yet ready for entering, though there is completion certificate issued by the authority. While paying the balance amount, I had requested them to remove the late payment charges, which they imposed as the rest of the amount was late. Also, asked them that since there is a delay in possession, I'll also not demand from you the compensation. The builder refused to pay compensation stating the "Non-timely" Payment from my side and asked to clear the late payment interest which is 15% per annum which is approx 2 lakh. I had tried to resist, but they are telling me to delay my registry by instructing their Lawyer. Hence, I think, i have no option than to clear the late interest amount & take the registry. Do we have an option to cancel my interest?