Unfortunately, this is a common problem and the advertising companies do little to correct mistakes or compensate their customers for the harm they cause. I have had clients, including myself, go through this exact same problem. You should not have to pay for defective advertising caused by your advertising company's mistakes.
The most efficient and cost effective way to resolve your dispute is likely the small claims court process. You can find information on the small claims process in Utah at this link: http://www.utcourts.gov/howto/smallclaims. In order to serve the small claims summons and complaint, you will need to learn the name and address for your advertising company's agent for service of process. You can find this information by searching the corporate records for your advertising company at the Utah Department of Commerce website: https://secure.utah.gov/bes/action/index.