Builder not giving flat after payment in full

I book sample flat 2bhk in 2017 december, by paying 50k in cheque with total sum of 27 lacs, flat was ready with some of the fitting and kitchen work was pending as per builder, i paid 25 lacs to him thru online and cheque , but builder gave receipt of 2.5 lacs only, and after repeated asking he did not respond on receipt. from 2018 i have insisting on Flat registration but Builder said, due to some problem registration is closed.and did not showed more interest in my flat registration. In 2019, He ask me to go for Home Loan thru Private finance AU Finance, which i did for 27 lac, and paid 3 EMI also. But as builder was not doing registration i cancelled the Loan. Now Builder is asking me more money against the Flat and further asking to take another flat with lesser area in different building. Which I denied. I have put my Furniture in 2018. builder has removed the furniture from that flat and locked it and kept his buidling material. WHAT SHOULD I DO NOW. I HAVE GIVEN IN WRITING TO HIM ON EMAIL ASKING FOR ALL THE EXPENSES INCURRED BY ME FOR NOT GIVING FLAT. PLEASE ADIVCE WHAT LEGAL ACTION I CAN TAKE