Request builder to waive penal interest for delayed payment

Dear Sir, We had recently purchased a residential apartment and had received the presanction letter from the bank with a clause mentioning clearance of credit card outstanding before 2nd disbursement of the loan. The first disbursement was made to the Builder based on current slab completion and payment schedule. On the next demand for the 2nd subsequent disbursement the payment from bank to builder did not happen as I was going through a financial crisis and could not clear my credit card outstanding as per the presanction letter clause which caused the initial delay. In matter of 15 days I cleared the obligation and started interacting with the bank for initiating disbursement after sharing statements and proofs against credit card amount closure. Then another 15 days delay from bank side happened in slow response and cross verification. Now due to the above, we are interacting on pending payments to proceed with registration and found out that the Builder has charged a penal interest charges at 18% as per agreement which comes to 10k. I would like to request the Builder to consider our situation and waive this fee. Request your advice on what would be the best way to convince and write an email to the Builder smartly to get this waived off. Thanking you.