Cancellation of flat

My father ragistered a flat in Amrapali river view project on 2014. After paying two installments ,my father died due to heart attack. We paid Rs 567000. After that, we could not paid amount due to sudden financial crisis. We cancelled the flat n they cancelled it and promised to return amount in short time. We have flat booking buyer agreement form n photocopy of payment reciept of installment n cheques. But, we were not given flat cancellation letter and recipient of submitting all original doc. for flat cancellation. But, they didn't paid amount till now. So, I called consumer forum and they said to send application to builder as notice for refund. Should I send application through lawyer or myself and what time limit should I mention for refundement in application? Are my documents sufficient or should I ask builder for proof of submitted doc and cancellation proof?? One thing is that the company is going through economic crisis.. Its amrapali group and is said to b bankrupt. Is it possible to recover our amount from such company through consumer court. Several other cases are also going on in apex court by investors whose huge amount sinned. Wat step sud we take?