I received ₹55,000 in cash as a token amount for two plots of land. I wrote "token advance towards sale consideration of..." on a plain paper and signed it. We had only verbal agreements about the sale. Now, I want to back out of the deal and offered to

I received ₹55,000 in cash as a token amount for two plots of land. I wrote “token advance towards sale consideration of…” on a plain paper and signed it. We had only verbal agreements about the sale. Now, I want to back out of the deal and offered to return the money. But the seller refused and sent me a legal notice claiming an agreement exists. What are my options? Is that plain paper legally binding? Can he pay stamp duty later to make it official?