GST applicability on prelaunch purchase of apartment

I made prelaunch purchase of residential apartment space of 1000 square foot from a builder in Bangalore in the year 2012 and made a payment of Rs. 30 lakhs for the apartment including PLC, Car park, maintenece advance etc. No tax was claimed by builder or paid by me at that time. A Memorandum of Understanding was signed by builder with me in 2013. Now the builder has started construction (2020/21) and send me a demand note for GST @ 12 % on the current sale price (in case he sales to a new customer an identical flat) of Rs. 40 lakhs and asked me to sign a term and conditions page. Now my questions are as follows: 1. Is GST applicable in this case and if so at what rate and on what amount? 2. If GST is not applicable, is any other tax (e.g. VAT, Service, Sales tax) applicable and again on what rate and on what amount? 3. Now the builder is calling the money I paid as EMD while in MoU it is clearly mentioned as 'Prelaunch advance full amount for purchase of 1000 sft apartment space' and I am defined as a purchaser. Is there any legal difeerence betweeen EMD and expression in inverted commas above and is that a serious matter and which one is beneficial to me? Thanks a lot for your kind guidance and help.