If the person upon whom the copy of such order shall be served at any time before the expiration of said 30 days, by a written notice served upon the commissioner or commissioners, deny such encroachment either in whole or in part, or shall deny the existence of a highway where such encroachment is claimed to exist, the commissioner or commissioners, instead of proceeding to remove such encroachment, shall commence an action of trespass against the person upon whom the copy of such order was served, as hereinafter provided.