Any insurance company in any field of insurance should know better than to require you to see anyone to fix whatever your need for insurance is. Car insurance companies cannot require that you go to one particular body shop and health insurance companies cannot require you to go to any one particular doctor. This is another form of Medicare supplier fraud that is becoming an issue, when suppliers are requiring participants to see specific doctors before receiving any further materials.
What insurance companies can do is recommend someone to you that can help you with an issue, but requiring any one person or place is a conflict of interest. You have the ultimate right to decide who will help you with your issue and if you choose that person to be different than the insurance company so be it. Your right as an American is to treat yourself the way you wish to be treated so you can do the same with your insurance.
Any supplier that tries to force you to see one particular person should be reported to the Medicare authorities to be handled immediately. This is not a practice that Medicare makes regular habit so you should not expect that you will have to go to anyone to get supplies. Direct your questions about care to your healthcare provider to guarantee you are getting the care that you need.