How would I report a possible faulty pump at a gas station?

My tank was less than a quarter full, but the light hadn't come on indicating about 3 gallons remaining. When I filled up, the pump said it took 16 gallons, but it only holds 17 and I think I was ripped off. How can I request a regulatory agency to check the station? Mobil station in Yorba Linda, CA at Yorba Linda Blvd and Richfield.