Ohio Rev. Code § 4905.32: Schedule rate collected.

No public utility shall charge, demand, exact, receive, or collect a different rate, rental, toll, or charge for any service rendered, or to be rendered, than that applicable to such service as specified in its schedule filed with the public utilities commission which is in effect at the time.

No public utility shall refund or remit directly or indirectly, any rate, rental, toll, or charge so specified, or any part thereof, or extend to any person, firm, or corporation, any rule, regulation, privilege, or facility except such as are specified in such schedule and regularly and uniformly extended to all persons, firms, and corporations under like circumstances for like, or substantially similar, service.