Any insurer or rating organization aggrieved by any order or decision of the commissioner made without a hearing may, within 30 days after notice of the order to the insurer or organization, make written request to the commissioner for a hearing thereon. The commissioner shall hold a hearing within 30 days after receipt of the request and shall give not less than ten days' written notice of the time and place of the hearing. Within 30 days after the close of the hearing, the commissioner shall affirm, reverse or modify his previous action, specifying his reasons therefor.