Sell the property after getting the notice from the district court

I wanted to sell an empty land and had an agreement on a plain white paper with a buyer in Feb, 2020. The property is in Karimnagar district while I reside in Hyderabad. The buyer gave me 1L as advance. He then failed to give the remaining money as prescribed in the agreement. When I called up the mediator he mentioned that buyer will not be going ahead to buy the property. In Aug, 2020 I found another buyer and entered in to an agreement with him. He did pay a portion of the price as per the agreement and is on track to pay the remaining amount. The registration is due in a month (like Feb, 2021). The first buyer started calling me from Sept, 2020 onwards to sell the property to him as he now wants the property as it is close to his parents house. I informed that I have already entered into an other agreement and cannot sell the property to him. I also told him that I will return 50K from his initial 1L advance as a good will although there is no legal binding. He served me a notice through the Karimnagar district court that I have cheated him by not selling the property to him. 1) Since the agreement was written on a plain white paper does it hold good in the court? 2) Can I still sell my property while I got the notice through District court? The notice has allegations from the buyer but not any order from the court. 3) The notice has false allegations that he constantly called me from Feb, 2020 asking me to take the money and claimed that I denied taking money from him. I do have a phone recording that clearly captured him saying that he lost the agreement document in Mar, 2020 itself and did not have my contact to call me since then. He found the document only in Sept, 2020 during a house renovation and called me only in Sept, 2020. What can I do to make him realize the cost of lying in the legal notice? 4) What action should I take to stop him from interfering in selling my land?