Seller delaying the refund of advance money amounting to 19 Lakhs.

Hi Sir, I booked a independent house near Rampally, Hyderabad and paid token amount of 1 lakh initially to the seller. Later lockdown happened and then we had to wait for 3 months. Then in May when lockdown was eased we contacted the seller and he said work will resume now and again asked for some advance. We paid 11 lakhs cash and after some time again paid 7 lakhs online for which we have the bank receipts. When we applied for the loan in HDFC, the said the legal heirship document is missing and they cannot disburse the loan. I informed this to seller and he said there is no way to bring that document. Then I asked him to return my money, now he is saying after selling the building he'll return the money. But he is not giving any date. He is saying he spent the money which we paid and once the house is sold, then he'll return the amount. But he is not giving any specific date. I need some guidance on how to go with this and get the money back? The only problem is we do not have receipt for the cash amount that we paid. I have whatsapp messages and call recordings where he confirmed to have received Rs 19 lakhs from us. Please advise.