Cancellation registration of previous ATS between builder and 1st buyer pending

I am a resident of Delhi and bought a property in Bangalore for which I have entered into ATS with builder and have paid 100% payment to builder. The ATS is registered. Two days before execution of sale deed, builder requests to postpone the sale deed registration owing to some technical issues in documentation. I was expected to cancel my travel and accommodation arrangements without even informing the reason for delay. Later on pressing hard builder revealed that they had entered into registered ATS with another lady 2 yrs ago. However she lost her job in Covid and couldn't avail loan. As a breach of contract builder deducted 10% from booking amount and refunded the balance as per the ATS clause. However the lady filed a suit to claim the 10% but eventually lost the case. After winning the case only builder had offered the unit for sale to us.But as a process cancellation registration of that ATS is required which they haven't done. 1st buyer won't come for cancellation hence they have to do it unilaterally. Now builder is claiming they can do it unilaterally without any problem but it has been a month now since they have taken 100% payment. Still the status is same . Since I have taken loan which has also been disbursed, bank is also following up for sale deed. Pls advise what to do. Builder has requested for another 30 days time. Should I wait or take some legal action as i am losing interest money with every passing day