Wyo. Stat. § 37-2-218: Refund of excess charges.

Whenever any public utility shall charge, collect or receive any rate or rates in excess of the rates fixed in the schedule of charges then in force, as provided in this act, it shall be the duty of such public utility straightway to refund to the person paying such excessive rates the difference between the lawful rates fixed in such schedule and the rates so charged, collected or received.