Don't assume anything with the subcontractor, he may talk sugar but bare open available ground makes for easy digging. If this would happen on my property: I would send a letter to the company stating that the line is on your property without easement granted and that the boxes must be removed immediately, any future access for repair of the line, repair, adjustment, reading etc. of the boxes is denied without written approval of adjustment to the easement. This letter has far more influence when generated by an attorney. As a former developer and president of a HOA, it is prudent to act quickly, legally and in simple terms.