Issue with the property owner

Hello Sir/Madam(s), here i am providing my issue briefly. My father is a businessman having own shop. Around 10 years back we took a small room near our shop as a go-down on rental basis for storing our business related articles. In the mean time the owner of the go-down had taken money of around 5 lakhs from my father as a debt. After that we asked him about the money but he didn't repaid it and this process continued for sometime. In 2014 due to health issue he passed away. After that when we inquired we came to know that the property (go-down) is not in his name but in the name of his sister, so we met his sister and her husband several times regarding our money but there is no positive response from them. Finally we filed a case in the court regarding this issue around a year back. Recently when my father inquired in the register office we came to know that they sold the property to someone. This is the situation of the case. So if possible please help and guide us in this issue which will be very useful for us.