no person shall carry on the business of a stockyard owner or market agency unless the rates and charges for the stockyard services furnished at the stockyard have been filed and published in accordance with this section and the orders of the Secretary made thereunder; nor charge, demand, or collect a greater or less or different compensation for such services than the rates and charges specified in the schedules filed and in effect at the time; nor refund or remit in any manner any portion of the rates or charges so specified (but this shall not prohibit a cooperative association of producers from bona fide returning to its members, on a patronage basis, its excess earnings on their livestock, subject to such regulations as the Secretary may prescribe); nor extend to any person at such stockyard any stockyard services except such as are specified in such schedules.