Purchaser Not Cancelling The Unregistered Sale Deed Even After 21 Months

I had an unregistered agreement of sale for an unapproved plot for Rs.3150000/- on 23/02/2019 and the agreement has a clause that the agreement is valid for 3 months. I had received Rs.500000/- as advance. Property has a problem in measurement, though the total area is the same which I have informed purchaser orally before the agreement and he had no concern on that problem. I also have a clause that I can forfeit his advance if does not purchase the property within 3 months from the date of the sale agreement. But purchaser has not purchased the property even after 1 year. I sent notices to his residence. He has changed his residence mentioned in the agreement and notice is not delivered. Notice sent to his office returned with the reason that there is no person by that name, though the person's name and address are correct. Somehow he has managed to return the notice sent to his office. I sent an image of the notice through WhatsApp which has 2 ticks with blue marks.