Thanks for all the responses.

So we went out there this evening and did some measuring between the marker pins. The pin in question has definitely been moved about 19 ft. due south and by doing so, they have added about 20 ft of additional culvert. The gravel driveway, which is kind of roughly put down, goes over the property line maybe a foot. This is based on the flags around the trees and where we think the corner maker was at.
So now the issues are the marker pin for the corner of the lot has been moved about 19 ft to allow them to put in another section of culvert, and the new culvert crosses out property line by about 10 ft (this happens in the utility easement ) See the attached sketch which sounds the pin that has been moved due south, parallel to the road. While we're waiting on the contractor to respond, we're consulting with a lawyer. I can't seem to rotate the image. In what is shown the pin has been moved to the right. Our lot is #7, there's is #8