As the Supreme Court held in Gwinn v. Alward, 235 Va. 616, 621, 369 S.E.2d 410, 412 (1988), ???the decision by the zoning administrator that [the land owner] was operating .?.?. on the property in violation of the zoning ordinance was a thing decided and was not subject to attack by [the land owner] .?.?. because [the land owner] never appealed the various decisions in which he was declared in vio