Builder asking to pay more amount then mentioned in agreement

Hello Sir, I booked Under construction property in Mumbai and I have paid 25% to Builder. My property value in 48,00,000 and I paid 12 Lk. according to agreement I have to pay 15% on plainth. My Pre-Approve Loan amount is 28 Lk and I asked Builder for NOC for proceed further loan process. But Builder is refuse to provide NOC and he told me to pay balance amount i.e. remaining RS. 8,00,000 and then we will give you NOC for Loan process. Building is 17 flowers and work is done only Plinth. Is this demand is correct or wrong? please advise.