Additional Deman by Builder

Hi, Builder told me that I had to pay additional amount of Rs 76342 including interest amount of Rs 5842 for the delay of last payment for three month only for Rs 173000 which was delayed only because builder not mentioned the actual flat price prices in allotment letter with including GST and bank given loan amount accordingly but later one I asked bank to do top-up to complete the payment and also given me the break-up of amount on A-4 sheet paper even not on company’s letter. Though he still not confirmed whether he got occupancy certificate but forcing me to pay that amount in order to get possession otherwise they will not give me possession letter. Flat is under "Affordable Housing Scheme". Break-up of charges:-(322 SQFT) Utility Connection Cost-40Rs per SQFT=12908 Rs Common Area Power Back-up-25RS per SQF=8067 Meter & Load-95RS per SqFT=30656 Fire Fighting Charges-25RS per SQFT-8067 Advance Running Cost- 10800 Interest-----5842 Builder demanding the amount as per below clause of agreement:- Developer obligated to pay EDC to `DGTPC in term of licence. The purchaser has agreed to pay EDC charges in respect of carpet area of flat at such rates may be determined by developer and informed to purchaser. I have filed cases in RERA today but please suggest.