Issue related to Advance token/Bayana amount repayment or forfeit.

I was intended to sell my house. After the initial talks with her (buyer) sales consideration fixed Rs.40 lakhs. I've shown all the previous original copy of Power of Attorneys. She paid advance Token/Bayana of Rs.4 lakh cheque on 31/01/2019 and balance within 6-month as per agreement to sell and purchase. On 20/06/2019 I received ‘legal demand notice to cancel the agreement to sell and purchase and to recover the Bayana amount/part sale consideration amount’ from her advocate and made these baseless and false allegations: 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 for last decade and already bought a plot in the same colony and know that all colony in Narela are unauthorised.