I have BlueCross BlueShield supplement to my medicare. My plan is a Regional PPO!

Recently, my chiropractor's ordered an MRI and his insurance clerk set up the appointment. I told her my plan was a networked PPO. She also had made a copy of my insurance card. The appointment was made for me at an imaging center, and I paid $100.00 co-pay. Today I received paperwork from BCBS, and it looks as if the facility was out of network and I will have to pay over $400. Isn't it the responsibility of the insurance clerk to choose an MRI facility that was in my network? The card says "Regional PPO." I had mentioned to the clerk I had a PPO plan, and I am pretty sure I told the facility when I called them. Was it my responsibility to have checked with the insurance company myself? Or should I have relied on the doctor's office to have chosen a facility within my network? There are several in my city. I learned after the fact, unfortunately. Usually, I do check myself online to see if the doctor is in my network, but this time I didn't because I thought the clerks knew what they were doing. I had discussed my plan with them. Do I have any recourse?