No utility shall abandon all or any portion of its service to the public except ordinary discontinuance of service for nonpayment of charges, nonuser and similar reasons in the usual course of business, unless and until written application is first made to the commission for the issuance of a certificate that the present or future public convenience or necessity permits such abandonment and the issuance of such a certificate. Upon the filing of such application and after a hearing of all parties interested, the commission may or may not, in its discretion, issue such certificate.