ellenrr
Do not give up yet.
If you made a switch from a private Medigap plan to a public Medicare Advantage plan FOR THE FIRST TIME sometime in the last 12 months you may be able to switch back. Also. if you received bad advice from a SHIP volunteer at the senior center, you may be able to switch back. See special situations at this government web site: http://www.medicare.gov/sign-up-change-plans/when-can-i-join-a-health-or-drug-plan/special-circumstances/join-plan-special-circumstances.html#collapse-3221 And of course you can switch back next year.
Also you may be able to negotiate a deal with your therapist to pay him or her cash with the money you are saving by having no supplemental premium this year. And you can go to a therapist that is covered by AARP.
However, when you switch, get good information this time. There is some bad information in this thread and elsewhere on the Internet. Trust medicare.gov (in the rare case that it's wrong, you have proof that a federal employee gave you bad advice and can almost always then reverse the choice). Both the public Medicare Advantage approach and the private Medigap approach to supplementing Original Medicare Parts A and B have pluses and minuses.
The public Part C Medicare Advantage approach is typically but not always a classic HMO, what is being called an accountable care organization by Obamacare. HMOs and ACOs are the wave of the future supposedly because you get coordinated care from a primary care physician. Some Medicare Part C health plans are PPOs, not quite as coordinated but still coordinated. It is not a case that your new AARP insurance replaced your Medicare (in fact you have to be on Original Medicare Parts A and B -- and keep paying your B premium -- in order to sign up for Part C) but just a case that your therapist is not in the HMO or PPO. You are right that your SHIP volunteer should have explained this and if she or he did not, this alone might be grounds to allow you to switch back right away. Medicare Part C plans are also geographically restricted to your local region for normal treatment
But public Part C Medicare Advantage has some important advantages too. The most important is that all Part C plans offer catastrophic coverage. Original LBJ Medicare does not. Most private Medigap plans do not. Also as you found out, most Part C plans cost less than the combination of Original Medicare and a private Medigap plan and offer more services, such as dental and vision coverage but also usually drug coverage, annual physicals and even coverage outside of the U.S. (I'm not suggesting that you're considering the grand tour but -- depending on where you live -- you might want to head over the border to Nassau, Niagara Falls, Vancouver or Mexico for a few days vacation. Original Medicare and most private Medigap plans will not cover you if you take such a mini-vacation and get sick--even in an emergency.)
Private Medigap plans offer the reverse. They typically cost more but let you go to any doctor that accepts Medicare, like -- apparently -- your therapist, anywhere INSIDE the United States ANYTIME without a referral from a PCP. Great if you spend the winter in the south and the summer in the north. Also can be a good deal if you don't have a lot of medical issues and no drug needs (take the cheapest Medigap plan and no Part D).
Like everything else in life, it just depends.