Original suit Money - ex parte evidence - execution petition

I have purchased a housing plot on Nov 2012 from owner B . B has purchased this plot from owner A in Jan 2012. It seems owner A made a unregistered sale agreement with party X for this plot and made advance payment 1 lakh in Feb 2011 with 3 month validity.But failed to register and agreement elapsed. Later Party X has claimed 1.5 lakh from owner A indicating that he has done some development works in that plot. I was unaware about these issues and same as owner B. We purchased the property as per registered with clear encumbrance certificate. It seems party X filed a money suit on Nov 2014 mentioning defendant 1 as owner A and defendant 2 as owner B and myself as defendant 3 claiming the money. The case was ex parte evidence on Sep 2015. Again party X filed EP on Jan 2016. Now I have received court notice for hearing. Please note that I am NRI I left India on Aug 2014 and came back on Apr 2016. I was not present in india during the case tenure. Kindly advice what I can do further and if I appeal can I clear this.