Hi, @phoenixpal – I have been a Mayo Clinic patient in the Rochester, MN area since the late 1970's but I did have some billing issues for a short time when my employee HMO did not have Mayo Clinic as my in network provider. Once I switched over to a plan with Mayo as the in network provider I had no problems. I really think a lot of the billing issues are due to the insurance companies. I'm now 76 and have a Medicare Advantage plan (MN UCare) and it is great. I have a $20 copay for regular appointments and recently had a TKR which was covered really well and didn't cost much out of pocket for me. My wife also has Mayo Clinic as her in network provider but has BCBS through her job but her coverage is not very good...but then with her good health it isn't quite as important for her.

I've never had just Medicare insurance with no other coverage as I don't think it's that good (just my opinion). Do you have an insurance adviser that can help explain Medicare billing and charges? Medicare also has some online information that may help:
https://www.medicare.gov/your-medicare-costs/get-help-paying-costs
Also, have you talked to the Office of Patient Experience about this issue? I wonder if they may be of help. Here's their contact info: https://www.mayoclinic.org/about-mayo-clinic/patient-experience