It is basic law that a tenant cannot stop the landlord or his agent from selling the property which he occupies as a tenant. On the sale of the leased property the tenant becomes a tenant under the new owner i.e the buyer, whereas his tenancy does not come to an end with the execution of the sale deed by the erstwhile owner. The new owner steps into the shoes of the previous owner in so far as the lease deed executed by the latter in favour of the tenant is concerned. So you cannot challenge the sale deed executed by the GPA holder for and on behalf of the landlord. Your only remedy is to restrain the owner from evicting you without following the due process of law.