[Resolved]  Tata Housing Development — why 18% gst on club house that was completed before gst was announced?

Booked a 2 bhk in tower 9, tata ariana at kalinga nagar in bhubanesar in march 2016 by 30 :70 scheme and have already paid 30% equal to almost 19 lakhs. However, as this is an under contruction property, it attracts 12% gst for the remaining 70% that is to be paid in december 2017 even though 70% of tower 9 has construction has been completed before the announcement of gst. The company claims it has received no input credit hence the 12% gst is to be borne entirely by the buyer. However, the club house has been completed before the gst announcement, so why levy 18% tax on that? Why should customers have to bear the increased amount? According to gst, builders cannot increase the price of an under construction house inclusive of tax. So why are buyers being made to bear the entire 18% gst on the club house that has been completed before gst? Why are buyers of tower 9 bear the entire 12% tax on bsp when they should be levied 12% only on that phase of construction that occurred after the gst was announced?