To refund the advance amount

I decided to purchase a resale flat which is still under construction . I booked it by an advance amount of 3 lakhs 50 thousands on 17th March 2020. I had to take loan from bank . But again and again the agreement which was made by the builder shows some fault by bank. So it rejected. At last the builder says to take a lawyer and make a new agreement. So we did it. And the fresh agreement was signed by us and seller and also builder and so on others as per rules on 27th of March 2021 and submitted to bank on 30 th March 2021. And and bank took 20 days to sanction. But in the mean time just after sanction has been issued by bank on 20th April the seller claimed an extra charge of 3 lakhs as they shows they have also loan of that flat and for delay of the loan to disburse. And also they want to cancel the deal and claim that we have to pay 10 % of total flat value to them. In this situation my question is that who were to responsible to make a sale agreement as it was a tripered agreement And we did not want to cancel. They only want to cancel . So how could I get my advance money ( 3 lakhs 50 thousands) back and is there any rule as per HIRA that they could claim of 10% amount of total flat value from us?