Builder send intimation of cancellation letter

Dear sir I Karan gupta booked flat in suntack maxx world underconstruction ( nai gao Mumbai) Maharashtra in Feb 2020 and booked by paying 5% amount via NEFT. In lockdown my wife lost her job in may 2020 After that I tried to loan bus loan rejected due to income issue. Currently builder demand more 30% Flat possison date is 2024 Jun. And builder sent me INTIMATION of Cancellation letter and said pay in 7 days else we will cancel booking and will not refund 5 % booking amount + stamp duty and registration charges ( which is not done ) I have only paid to builder . But now hdfc bank said will provide loan because my wife joined job in last week . Now be both having job. Now my question is 1- builder have right to not refund my stamp duty charges ? 2- builder can now send me cancel letter and I will lost my money.? 3- if in 30% I will pay more 10% by own fund can if any condition loan failed the. Builder will refund or not my 10% + stamp duty ?? 4 - by sending 1 letter builder can cancel deal ? Thank you sir.