Is a property sold through an unregistered agreement legally valid?

An unregistered agreement to sell doesn't, by itself, transfer ownership of immovable property to you — for the actual transfer of title, a registered sale deed is generally required by law. What you likely have at this stage is a contractual right to eventually have the sale completed, not ownership itself.

Depending on the specific terms of your agreement and how much has actually been paid, you may be able to seek specific performance — a court order compelling the seller to complete the sale and execute a proper registered sale deed — if the seller is now refusing to cooperate.

Whether specific performance is available, and how strong your case is, depends heavily on the exact wording of the agreement, proof of payments made, and whether you've fulfilled your own obligations under it. It would be important to consult a property lawyer promptly with your agreement and payment records to assess the best way forward, since delay can sometimes weaken this kind of claim.