A few years ago my insurance did the same and my dentist dropped out. I had to find a new one. Took me 15 tries with each one being a new office, cannot use old office info/x-rays/etc. Cost the insurance co. a nice bit of change to cover it. When I was confronted by them on it, I explained if they hadn't changed what was covered, I would have stayed with my old provider. Now they get to pay til I find one I like. Or they can opt to pay what they used to pay.