Sale Agreement between New Landloard and Tenant

Hi Sir, I need your help on below queries. My father took a shop on securtiy amount of 40,000 Rs from a lady landoard in Delhi to run the small business around 30-35 years back with having conditions written on a paper and rent decided as per pagri terms & conditions. Long time ago Lady landoard passed away and his son started taking rent from us. Now 1 month back he sold his property including shop which is in our possession to a new person. And that New purchaser has made an agreement with my father in the presence of old landloard to give the possession of shop to him after he settled the amount as decided between us. And later on new buyer has purchased the property from old landloard having registary of that home. Now time is near to make the settlement amount agreed by new buyer to pay to the tenant which he agreed with tenant to vacant the shop before registery. And now new buyer has changed his mind and decided to cheat and fraud with tenant to not to pay agreed amount on mentioned time and date as per agreement. He want to give just 30% of amount of settlement what he agreed in agreement. Can you please advise that what tenant should do against that existing landoard who has already sold out the property and the new buyer who is not willing to pay the decided amount to tenant per agreement. Isn't it cheating case against new landloard how he made the settlement agreement before registery and now he is not ready to give money as per agreement.