Section 4. Such company shall issue only such amount of stock and bonds, and of coupon notes and other evidences of indebtedness payable at periods of more than three years, as the department of telecommunications and cable may from time to time approve as reasonably necessary for the purpose for which such issue of stock, bonds, coupon notes or other evidences of indebtedness has been authorized. Said department shall on an application for such issue, within thirty days after the final hearing thereon, render a written decision assigning the reasons therefor, and, if approving such issue, specifying the respective amounts of stock, bonds, coupon notes or other evidences of indebtedness approved for the respective purposes to which the proceeds thereof are to be applied. The decision shall, within seven days after it has been rendered, be filed in the office of the department and a certificate of said decision shall, within three days after rendition and before the stock, bonds, coupon notes or other evidences of indebtedness as aforesaid are issued, be filed in the office of the state secretary, and a duplicate thereof delivered to the corporation which shall enter the same upon its records. Such corporation shall not apply the proceeds of such stock, bonds, coupon notes or other evidences of indebtedness as aforesaid to any purpose not specified in such certificate.