D.C. Code § 34-1129: Utility not to receive greater or less compensation than fixed in schedule.

It shall be unlawful for any public utility to charge, demand, collect, or receive a greater or less compensation for any service performed by it within the District of Columbia, or for any service in connection therewith, than is specified in such printed schedules, including schedules of joint rates, as may at the time be in force, or to demand, collect, or receive any rate, toll, or charge not specified in such schedules. The rates, tolls, and charges named therein shall be the lawful rates, tolls, and charges until the same are changed as provided in this subtitle.