(a) In any proceeding upon the motion of the Commission, or upon complaint, or upon application of a public utility, involving any proposed or existing rate of any public utility, or any proposed change in rates, the burden of proof to show that the rate involved is just and reasonable is upon the public utility.
(b) The public utility shall have the burden of proof in justifying every accounting entry of record questioned by the Commission which may suspend any charge or credit pending submission of satisfactory and sufficient proof in support thereof by the public utility.
(c) The Commission shall give preference to the hearing and decision of any rate proceeding over all other proceedings and decide the same as speedily as possible.