I have been fighting with Medicare Advantage plan, Preferred Care (owned by United), as they do not honor their responsibilities, as outlined by Medicare. In addition, when I contact Medicare, depending on "person", I get someone helpful, but have to allow 30 days for insurance co to respond, then when I call Medicare back, they say they have no authority on Advantage Plans??? In the meantime, my father is being denied NEEDED care.
So are you talking about an Original Medicare service or an additional service you think the policy says is covered? Once you are sure it one or the other, you have to follow the steps outlined in the insurance policy for appealing its decisions (which are basically the same as the procedures in the Medicare and You booklet).
However as someone else has noted, if this is for a medical service that neither Original Medicare or the Advantage insurance covers, you would be wasting your time.
You need to drop this plan and pick up another "Advantage Plan" that has the benefits you want. Look at Anthem, Humana, Aetna or AARP. ehealthmedicareplans will help you compare plans.
Another option is to get "original" Medicare with Medigap (also called Medicare Supplement). Read everything on medicaresupplement
Remember agents get commissions and give kickbacks. So they are not necessarily in your corner.
They can assist hands on to resolve your issues with MEDICARE, SUPPLEMENTS, & ADVANTAGE plans. They also assist finding a new plan if your are unhappy with the one you have.
A long shot, and perhaps questionable in terms of your specific situation, is to also research locally and nationally as to whether United has been sued for similiar behavior and lack of cooperation. If so, you might want to consider consulting an attorney for some extra legal muscle in dealing with United.
If you don't mind the publicity, you can reach out to media, such as local news channels. They enjoy coming to the rescue of citizens battling big business.
In the meantime, I would start researching Medigap or other plans. The kinds of problems you're having are a primary reason why we've stayed away from these companies that repeatedly send out solicitations and actively recruit clients.
If your dad needs Home Health Services then you do need to have an order (or prescription) from his doctor stating he needs those services. Home Health Services usually covers services from a nurse, home health aide, medical social worker, PT, and OT. If your dad needs regular in-home attendant care (help with activities of daily living) then this is different from Home Health Services. These are the services that may not be covered by his plan. These services are sometimes covered by Long-term Care Insurance or Medicaid if he is low income. A Vet can get these services under the Aide & Attendant Program. Medicare does not cover long-term care. Good luck!