Whenever the public utilities commission is of the opinion, after hearing had upon complaint or upon its own initiative or complaint, served as provided in section 4905.26 of the Revised Code, that the rules, regulations, measurements, or practices of any public utility with respect to its public service are unjust or unreasonable, or that the equipment or service of such public utility is inadequate, inefficient, improper, insufficient, or cannot be obtained, or that a telephone company refuses to extend its lines to serve inhabitants within the telephone company operating area, the commission shall determine the regulations, practices, and service to be installed, observed, used, and rendered, and shall fix and prescribe them by order to be served upon the public utility. After service of such order such public utility and all of its officers, agents, and official employees shall obey such order and do everything necessary or proper to carry it into effect. This section does not give the commission power to make any order requiring the performance of any act which is unjust, unreasonable, or in violation of any law of this state or the United States.