Does anyone know if there is such a thing as a Medicare advocate?

Who is able to help folks through unusual Medicare challenges? An Anomaly has appeared on my Mom's Medicare and somehow, her primary insurance Medicare, was put as secondary and her secondary as Primary. This has caused numerous denials on her recent medical bills. We are slowly getting this back to what it has always been since 1984, but having an "expert" advocate to do some of the calling and advising us would be a wonderful aid for when these challenges arise.