Received a Notice from the Buyer

Sold my flat in the month of November 2022 ,at the time of buying a flat ,the buyer requested me to mention in the agreement of amount 30 lacs only and rest 30k he will pay in cash at the time of registration which is not mentioned in the agreement anywhere.Now as the flat is in the housing complex he received the unpaid CAM bill of INR 39000 which was intentionally not paid by me as I was aware that he will not be giving any amount post registry.And at the same time on a good faith I have left my Modular Kitchen,TV Unit, Geyser, Iron Balcony Grill and LED light at the flat.Now he has sent me the notice through advocate that if that dues is not cleared in next 7 days then he will be taking legal against me.Suggest me at this situation what needs to be done with such fraud person