Sale of property and possession given but registeration to be carried out later

Original sale agreement has taken place on 07/09/2012 between Shri Rakesh Khattar (the seller my uncle) and Smt. Saroj Rani Manchanda (the buyer) in which actual sales consideration was Rs.14,20,000/- out of which only Rs.20,000/- has been accepted in cash and the balance consideration is taken by account payee cheque and the possession of such property also taken in same year. Both parties went to registrar for registration of such property but as some of building norms was not completed and some objection from civik agencies the registry of such property has not taken place. The possession had taken place in the year 2012 only what is left is the registration of said property with the registrar. In the year 2016 the buyer has completed all the formalities and taken NOC from civik agencies and both the buyer and seller went for registration of the said property with the registrar but in mean while the circle rate of the said property were increased from Rs.14,00,000/- to Rs.21,00,000/- What should be done???