Sounds like you have an advantage plan. You get PPO or HMO from advantage plans and the limit the coverage area and usually have a poor selection of docs and facilities that are in network.
I am getting rid of mine and switching to a medicare supplement/gap plan that covers 100% of the bill and is good anywhere I go. Get your plan from a broker or go online and sign up. AARP adds a markup to the coverage you get from them so they can give you a discount and you end up paying what other plans would have charged without going thru AARP.