Landlord vs tenant

We had paurchased Industrial Gala in 2010 feb from the tenant at Rs. 30 Lacs. That time the another person who have the power of attorny from our old landlord issued us the rent receipt and he had taken some amount from the seller of this gala. Then our old landlord sell his property to new one. Actually our new landlord says, they had done their purchase procedure in December 2009. Before some months we tried to contact our new landlord to take the rent of Six years and issue us rent receipt. Then our new landlord says, we had not received any details from the old landlord which proves you are our legal tenant and therefore we can not accept the rent from you. New landlord frequently send the notice and he is saying that you have tresspassed the said gala. He is asking us to show any legal proof but we dont have the old landlord signs on the papers made between seller and us. We have one old rent receipt of march 2009 taken from our old landlord. Pl share ur best advise for this problem.. Awaiting yours..