There must be indemnity clause in your sale deed 

2) it would indemnity you in case any claims are made 

3) you can sue seller to recover your money with interest 

Issue a legal notice to seller through an advocate and file recovery suit along with interest. 

First, you decide exactly from whom you want to take suggestions because we all are lawyers and not layers ?

1) Yes you can challenge this cancellation order passed by court.

2) You can ask court that what is your fault that you have purchased land from C. Kindly have mutation papers from last 40 years plus so you can understand it how the ownership got transferred.

1. If the sale deed between A and B is cancelled then valid title passes from C to you .

2. However it is to be seen what sort of suit it was wherein the court cancelled the deed between A and B.

3. If that point of time C was already purchaser then C was necessary party in the suit and  the decree was not binding upon C and hence upon you as well.

4. However before making final advice on this issue it is essential to see the decree itself.

5. Else you can seek refund of your money from your seller who in turn can claim the same from C.. 

Are you a participant in the court case?

Whether you have been impleaded as a party to the court case?

You have a registered sale deed, whether this was disputed in the court by any party?

If nothing stated above happened then what is your problem?

Did anyone ask you to vacate the property?

If at ll there is any notice received from anyone in future then you may dispute their claim and approach court based on the registered sale deed standing on your name for justice and releif.

Even if it is challenged you will have an upper hand that the said property was sold to you by way of fraud and misconception

1. Cancellation of the sale deed of a previous buyer would mean that the title of all the subsequent buyers falls like a pack of cards. 

2. Obtain a certified copy of the judgment of the court through which the sale deed in question was cancelled and then chalk out your further move.

You are in active possession of property since 2003 and without making you party in a suit, no adverse order effecting  your ownership is valid. 

What is order of court? 

After order,  party will file execution petition, at that time you can file your objection.

It depends on speaking orders (grounds)

See if the link document is cancelled and the person from whom you purchased his sale is also invalidated then your sale deed is also not valid.

If the case is A sold to B and B sold to C and then you purchased from.C then your sale is also not valid the actual owner can file for possession. Though in the suit you were necessary party and you were required to be made party.

1. I believe that you got your sale deed registered before the registrar’s office of your district where the property is situated.
2. And it holds your sale deed valid irrespective of the fact that there has been another sale deed (stands cancelled now) after few years from the date of the registration of your sale deed got registered.
3. You are in possession and if someone would come to evict you then file a police complaint against that person.
4. And if they wish then they can approach the court of law to prove that you are illegal occupants over the land and then you should contest it.
5. But, possession will not be taken from you as it is in your hand and you have all the required papers which are necessary to prove your claim as valid in the eyes of law.