No common carrier by motor vehicle, the rates of which are subject to regulation under the provisions of this chapter, shall charge, demand, collect or receive a greater, less or different compensation for transportation or for any service in connection therewith between the points enumerated in its tariff than the rates, fares and charges specified in the tariffs in effect at the time. No such carrier shall refund or remit in any manner or by any device, directly or indirectly, or through any agent, or otherwise, any portion of the rates, fares or charges so specified, or extend to any person any privileges or facilities for transportation except such as are specified in its tariffs.
