We had a verbal agreement to selling a property and received an amount as part payment.?

However, there was no written agreement for the same. Subsequent to this, due to some reason, the other party withdrew their intent to purchase the property and wanted their money back. Now, they have sent some letters which state false information by registered post which has to be acknowledged. Does receipt of these letters and not replying to them amount to agreement with whatever is stated in these letters? Do they have any valid grounds for legal action?