I am involved in a dispute with my general contractor. The work was performed on my coop apartment in Manhattan. The original signed contract stated "if there are any change order forms will need to be paid in advance." I was assured that a few last minute items would remain under $10,000 and I asked repeatedly for a change order but the contractor did not provide and executed the changes. Upon completion I received a change order for roughly $40,000 and thee detailed scope included many items that I believe were covered in the original scope. We could not reach agreement and today I was notified that there is a mechanics lien. Am I responsible for the change order? How can I best dispute this?