Litigated property

I own a property at kolkata, whose market valuation is 90 lakhs(as shown in the online market valuation property site by govt). But few years ago, my son took a loan from bank by forging my signature and bank too gave the loan without any physical verification against it. And now from last 8-9 months he has left the house, living somewhere else and stopped re-paying the loan amount. Now bank has sent the letter for further action of loan settlement. By managing them they have settled at 5 lakhs. As bank is also at fault and I cant file DRT against bank which require lot of money because i am retired person. My questions are: If govt. Valuation of property is around 90lakhs then why i am not getting to selling off the property at 60lakhs, i have already reduced the amount because of litigation. Is there any govt. Litigated property buyer who can buy this kind of property, if yes where can i get them? If no, then how can i sell this property off ? Please help me .....