Builder Not Giving ITC Or 1% GST Ben.for Underconstruction Flat Bought In July18

I have bought the Under construction flat in July 2018 under affordable housing at 8% GST. At that time we were not knowing about ITC(Input tax credit) builder also not told us about that. In April when the government stopped the ITC and put the 1% GST for affordable houses, we got to know about the ITC. As builder was not giving the ITC benefit previously we asked him to pass the benefits. But now builder is not ready to pass the ITC benefit and nor he is ready to take 1% GST for the remaining amount that is left. Builder is saying as per the agreement he is not liable to pay the ITC benefit to me. Also, he is constructing 7th-floor extra while in my agreement it is clearly written that builder cannot create more than 6 floors. Could you please suggest whether the builder is liable to give ITC benefit or 1% GST if I bought the flat before 1-April-2019. and if he is still not ready to give the benefits then in both the cases where should I complain and what is my legal rights.