1. A registered sale deed can be executed by the owner to the buyer and not the buyer can get the sale deed executed by himself/herself.
How did the tenant sell this property to you without having marketable title?
The sale by the tenant is invalid and illegal.
Execution of registered power attorney deed by an agent to another agent is also invalid and not maintainable in law.
You catch hold of the tenant who sold you this property to execute a registered sale deed in your favor or to return the money received from you by him.
2. The landlord need not reply to anyone who claims ownership, it becomes the duty of the person who sold you this property to get the property properly executed in your favor by approaching the original landlord.
Even the higher authority of this landlord cannot help you or rescue from this crisis because you have no authority since this purchase itself is not proper and invalid in law.
3. Dont get into any such wild imagination. What do you mean by paying 100 months rent? Is there any such agreement in vogue?
4. A tenant is always a tenant.
Just because you pay tax, you cannot claim ownership.
You may consult a local advocate and seek his advise to tide over the crisis after producing the relevant documents before him.