Cancellation of flat

Sir, /Madam. In 2017 I had booked a flat from Sowparnika builders in Bangalore by paying them 1lakh as booking amount, after 3 months I signed the agreement, and I started to pay them in instalments, I had payed them 11lakhs of rupees till December 2018 after that I could not do the payment because I had some financial problems I told them they said if you have to pay interest since the building was still under construction I said I cannot pay interest give me some time at the time of possession I will pay the full amount, they didn't agree for that they said you can cancel it, then I agreed for cancellation. This apartment was under Rera act. As it was in the agreement they said they will forfeit 1lakh, I agreed for it because I had signed the agreement, the same agreement stated that in case of cancellations the builder is to refund the remaining amount in45 days. But this builder has already sold that flat to another person and he has not refunded my money it is almost three months now. What should I do to get back my money. Can you please help me by your valuable suggestions.