Subvention scheme

Hi, I have taken a flat in 2016 in noida extension, under subvention scheme (5% Down payment +75% from Loan, 10% at final payment). After scheme expired the builder unable to handover the flat and for avoiding his mistake he floated the offer of Possession. For avoiding interest penalty. But later said he will not pay any interest on April-May 2017 payment. During that period i had a loan with TATA capital and they have very high intrest rate and easing burden i have switched my loan to ICICI bank. But ICICI bank only give loan on 80% of property value. For transferring the loan i made a part payment on June 2017. Now when i asked builder for final demand he said he will not give me interest from april 2017 ownward as i have made payment in there system. It is very said to here this as he had not given possession on time and for lowering my burden i have manage money and transfer my loan to the other bank. Now is not honoring subvention plan. Please advise what should i do to get interest amount from builder. Thanks.