@john123 I would certainly contact Mayo. This is from their page re insurances accepted at Mayo Scottsdale:
"Commercial Insurance Plan Contracts
At Mayo Clinic's campus in Arizona, Mayo Clinic providers and Mayo Clinic Hospital are contracted with the organizations listed below.
Your benefit coverage for care provided by Mayo Clinic is determined solely by your insurance company and is based on the provisions of your specific medical benefit plan.
Please contact the customer service department on the back of your member identification card to confirm if you have in-network access to Mayo Clinic, as well as your benefit level, for care provided at Mayo Clinic.
You may also contact Mayo Clinic directly at 480-301-7033, 800-603-0558 (toll-free) or 480-
301-7101 (international) for more details about the information listed below."

The link is https://www.mayoclinic.org/patient-visitor-guide/billing-insurance/insurance/accepted-insurance/contracted-health-plans
Blue Cross Blue Shield is listed there, with specific details.
May I gently remind you that the patient also bears responsibility in seeing that there is coverage, and indeed it may be a billing error.
**disclaimer: I am not a Mayo Clinic employee, nor a patient at any campus
Ginger