Legal proceedings against builder not refunding amount after cancelling the sale agreement

I have booked a flat which is RERA registered in Siliguri, West Bengal in February 2023 and paid 5 lakhs at the time. I also got the plan layout of how the final flat will be. paid again Rs 5 lakhs in December 2023. in December 2023 late that month found out that alterations have been done and the flat hasnt been constructed as per the plan layout and overall area of the flat has also been reduced by some 170 sqft approx. flat was then not likeable to me and i cancelled the agreement finally on 3 January 2024 verbally. builder insisted on NOC regarding not purchasing the flat. i gave NOC that he can show the flat to intended buyers only and the final NOC will be given when i will get my entire Rs 10 lakhs back. NOC was given on 8th January 2024. builder was like next week i will give u money, now this and that. a loan is getting sanctioned i will give from there and it was already march 2024. two months passed. after cancelling the agreement, booked another flat at another place and paid token amount too in January 2024. that new builder started asking for money. meanwhile the old builder giving excuses sold the aforesaid mentioned flat to a known person to me in March 2024 which i came to know much after. they paid Rs 9 lakhs in total to the builder but the builder even not informed me too neither paid a single paisa from that money. in april 2024 last week had a verbal argument and due to some pressure he paid Rs 5 lakhs after much arguments. again he paid Rs 2 lakhs in may last week after verbal argument and pressure. had a meeting with other partners then and everyone agreed mutually and the builder agreed to pay the entire money left of Rs 3 lakhs within 15 days. waited 15 days still the builder not paid a single amount to date. now again he is giving excuses that i will give money and unnecessarily avoiding it. i am a banker and the builder is having his bank account in our bank so i can see the transactions. he has got numerous loan sanctioned and disbursed to his account but he is still not paying money from it and doing RTGS and neft transactions to his suppliers. in the course of 15 days which everyone mutually agreed, the builder got a amount of Rs 7 lakhs as a loan disbursal which also he paid to some other supplier. kindly suggest me legal proceedings which i can intitiate against him. can i demand interest for these 6 months? since RERA says you have to settle the dues within 45 days and in the agreement it is mentioned that entire amount if cancelled will be refunded in 30 days. kindly suggest