Refund of advance money paid for a flat before signing the sale agreement

For buying a newly-built flat in a multistoried building, the developer (family partnership firm set up and built on their family land) took Rs 50,000/- cheque as advance before giving any document or draft agreement. He had said that the whole amount would be refunded immediately if I decide otherwise and won't sign sale agreement. Total consideration was decided at Rs 27,50,000/-. Subsequently, after realisation of my advance money, when the draft agreement of sale was given to me, some terms and conditions (on payment, access to common areas, area calculation etc.) written in it was against me and I requested to revise those clauses. They did not agree and finally they expressed their desire to go with other prospective purchasers and asked me to return the documents, which I complied. I sent them WhatsApp messages and informed over telephone about my no-objection to selling it to others. Initially, they sought one week's time to finalise with the new purchaser and then pay me but later they are not answering my calls nor replying to my messages or telling me to contact other family members. Two weeks have passed now but I have not received the refund nor any response. What to do? We did not sign the sale agreement. I have the payment receipt.