Sellers Refuse 1 week extension to close

[Adam Sanders]

I am trying to complete a one-time close construction loan in Minnesota. I enter into a purchase agreement on July 8th for the land to close on September 18th. The sellers were required by purchase agreement to provide a land survey.  They did not complete the survey until August 19th.  Now partly due to how late the survey was I need one more week to finalize everything, but the sellers are refusing to sign an extension.  What can I do?  Hire a real estate attorney?  Other ideas? Thanks for your help in advance