Builder asking for delayed payment charges

Hello Team We booked a 1 BHK Flat in Thane in 24th March 2019. For bank loan banker was appointed by him. Bankers refuse to make Loan because of cibil default. 2nd banker also appoint by builder and he also refuse to make loan and then he introduce me a new banker LIC Housing Finance on 5th June 2019. after that on 19th July bank issued me sanction letter. i visited to builder office on 18th July 2019 for payment and on 23rd august 2019 i made 5% down payment by bank transfer. Then i have received a letter from builder for interest on 20th August 2019 delayed payment suddenly talked with him and he promise me make a payment i will do something. registration done on 9th Sept 2019 and copy of registration papers i received from builders on 17th Sept 2019. on 15th October 2019 i make final payment and then till now he is asking me for interest on delayed payment charges. now its more than 45 days and we have not received possession till date what we can do in this case. Please help me out for this.