Issue related to Repayment OR Forfeit of Advance token/Bayana amount

I was intended to sale my house located in Narela. After the initial talks with her (buyer) the sales consideration fixed of Rs. 40,00,000/-. I have shown her all the previous sale documents (original copy of the power of attorneys) of my house. She and her family member visited many times before given advance Token/Bayana and after 1 month of checking or reviewing all aspects, she had paid advance Token/Bayana of Rs. 4,00,000/- through cheque on 31/01/2019 and the balance payment of Rs. 36,00,000/- payable within six-month time i.e. before 31/07/2019 to complete the said deal as per agreement to sell and purchase. On 20/06/2019 I received a ‘legal demand notice to cancel the agreement to sell and purchase and to recover the Bayana amount/part sale consideration amount’ from her advocate. In this notice she made these baseless and false allegations on me: 1. I assured that the abovesaid built up house following the site plan of DDA and falls in an authorised colony. 2. I also assured her that I shall obtain the NOC regarding the sale of said built house from the concerned department. 3. It was initially booked by the DDA 4. I don’t have proper legal sale/title documents in my favour. She lives in Narela with family for the last decade and she had already bought a plot of land in the same Sanjay Colony before approaching me to purchase my house and Neither me nor property dealer (who lives in the same Colony) told her that the said property is located in an Authorised colony, And her current residence is a 2 minute walk from my residence and She knew that in Narela all the colonies like Sanjay Colony, Rajiv Colony, Indira Colony, Punjabi Colony and Gautam Colony are unauthorised colonies.