Neighbor creating problem in making boundary wall

Hi I am Abhishek and I am a developer, I have been costtuted the power of attorney to promote a building by the landlord and sell it on joint venture basis. I have all the sanctioned plan by the municipality of Khardah , and all other relevant documents up to date with site plan approved by the same where the Arey of land is 2160 sqft and breadth of land is 8230mm that is 27 ft to be exact, Now there was a previous boundary wall and it was needed to be mend so it was to be re constructed that is why it was demolished first but the demarcated base of the boundary wall is present but one of the neighbor is claiming that they have 1feet of land has shifted into my property, they only have some xerox deed and one site plan mentioning the frontage of the property to be 50ft but the documents are not original and not approved, they might have an issue in measurement with another house present on the left side of them which is not my problem,, so What shud I do to give the boundary wall?