• Encroached land, no objection until house built

Hello,
I need an advice pertaining to a situation . I am explaining the points in accordance with the chronology.
1.A cooperative society sold land to one first party who in turn sold it to my father  also sold an adjacent plot to another person. Both the parties , the first owner before my father bought the land and the person who bough the adjacent land got the land registered somewhere in 1991.

2.My father bought   the 2800SQ FT from first owner and got it registered in 1998. 
3.The land was having it's boundary defined with brick walls at all the sides. 
The land has Road adjacent to it 25 ft on the east and 10 ft on the west. This detail is existing in the sale deed.
4. We started constructing our house in 1998 and built the complete house in 6 months and shifted to the newly built house on our plot. All taxes related to property were paid , were having landline connections on our name with the same address and electricity bill since 2000.. We were residing peacefully in this house since then.
5. In 2004 the party owning the land adjacent to my plot (a plot of 1440 sq ft on paper) sold it to another person . now this person never objected on anything since then.
6.Recently in 2014 , this person is claiming that his land was 1440 sq ft and in existence only 1000 SQ ft.
7. He claims that we have encroached his land.
8.The first party from whom my neighbor bought land never objected/claimed that we have encroached on his land.
9. My neighbor who owns the land since 2004 never objected until now about the encroached land for almost 10 years.
10. the land which my neighbor has bought in 2004 was having construction on both side, which in turn proves that it was pretty clear to my neighbor that in reality the land is lesser than the area recorded in his sale deed. and currently the land is in the same state as it was before he bought .
11. Now, recently he got the measurement done by the government amin working under regional circle officer, land deptmt. and this amin claims that we have encroached his land.
12. As per the map availble to amin which is an outdated survey map , we have shifted a bit inward from road towards his land which has caused the encroachment of my neighbors land.
13. We do not have construction beyond the total area on our recorded deeds and our construction is approved by the Patna rural Development (PRDA)
14. In main what my neighbor claims that we have shifted a bit inwards which resulted his loss of land and  in return he wanted us to vacate the land or pay him to the current market value.
15. we never intended to encroach his land and have surplus land beyond the constructed area so if my neighbor or the land's previous owner if anytime have objected to us about encroachment earlier then we would have easily vacated/stopped construction.
16. Now the house is completely built and we can't shift our constructed house. and the present market value of the land is sky rocketting which I am not willing to pay.

What should I do in this situation , Shall I approach court ? How strong is my case?

16.