Regarding my shop possession by third party

There are two shop one in my father name and one on my grandfather name. This property was bought by my father from palitana sugar mill pvt ltd, bhavnagar, gujarat.During that time they used to give receipt for that property. He was murderd in year 2000. And my grandfather is no more. But he has written a general will on my name. Now the document i have is light bill, muncipal kam chalav bill and my grandfather will. I dont have that receipt and i had approached several time 15-20 times where registration is done but they are not ready to give duplicate copy or for mutation. I have given notice and rti but they are giving no reply. And at present that third is holding that property and he has no document. He is crimal and telling us take 5 lakh and make property on his name. Or go and complaint to dsp or go to court and fight for 15-20 yrs. What should i do. Pleae reply. That propery is reistered on my father and grandfather name where registration is done. But they are not giving any duplicate copy. Can i and my mother go and break lock and board of that shop kindly help.