In that case whether the sale transaction between the parties( old and new landlords) is correct or not?
and whether the sale deed is null and void?, as the transaction was done concealing the fact that there is already a lease agreement exists in the property between the tenant and old landlord
The sale transaction between the landlords is legally valid but the previous landlord should have intimated you about this and also there should have been an agreement entered by him with the new landlord t this effect that to not to disturb your possession and enjoyment till the termination of lease period an to collect the future rents accordingly.
Since it has not been done by following legal procedures meant for it properly, you continue to pay the rent to yor previous landlord itself, if he refuses then you may aproach court seeking its permission to deposit in the court on the same ground. You do not have to bother about the new landlord or his dictates, let him approach court for his relief which you can challenge the same on the basis of merits in your side. .