Failure to pay the shortfall will result in CivilCase against u..

Hello Professionals, I had Home Loan in 2005 for 15 lac, started paying the EMI (averaged 15-17k) on time with some missed payments till 2010/2011, things changed, job loss, family financial situation we were unable to continue paying EMI hence defaulted, in 2014 bank took over and put it for auction and the property was sold in 2015 for 18lacs. I received notice to pay short fall of 5.5lacs failure which will result in Civil proceedings against u.. I sent the Bank a certified letter requesting them to waive the shortfall considering the payments made by us and the sale proceeds received by way of auction has covered the sanctioned amount and provided the bank with reasonable returns on its investment. 1. Kindly advice with your thoughts my situation and to what extend the bank can go to recover the shortfall. 2. How do you define shortfall in banking and Civil Law? 3. What should I do as I am not in position to pay the shortfall of 5.5 lacs, if we were able to we would still have the property with us. Thank you in advice for your time and response.