No payment by purchaser even after closed date

Sir pls help We have sell our property flat in mumbai to a purchaser and purchasers are working couple of age 24 both. They have given 50k token and then 7lac cash in month of dec when dealing was done they paid in cash due to loan agreement. And we purchased properrt outside mumbai by paying 11lac as a token in cash to builder being it cash builder havent given us anythng in writing. And now its almost 5 months the purchaser they havent paid us anythn nor their loan is happening since 5 months yes they arent quite eligible for it which they didnt clear us in beginning. Now they not giving us any solution what to do. Instead they sayinv now cancel the deal and pay us 7.5lac of ours what we paid. How is it possible we said as we booked our house from that money and now our builder has given us last few days to pay full amount otherwise he will sell the house and he wont refund us any money if we cancel the deal there And here our purchaser asking for full amount back as they want to cancel d deal which is their fault and after 5 months of deal how can i pay them full Need ur advice on this at earliest what should i do with purchaser