Under const. flat buy before 1-april-19 builder is not giving ITC benefit & not ready to take 1% GST

Dear Sir, 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. Now in April when 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 remaning amount that is left. Builder is saying as per the agreement he did with me he is not supposed to pay the ITC benefit to buyers. Also he is constructing 1 floor extra while in my agreement it is clearly written that builder can not create more than 6 floor while he is creating 7th floor. Could you please suggest whether builder is liable to give ITC benefit or 1% GST if i bought the flat before 1-april-2019 and if my DD(Demand letter) was given to me before 1-april-2019 by builder? 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.