What is the name of your state (only U.S. law)? CA
April 2010: Got new health insurance. Took daughter to doctor. Paid copay.
January 2012: Doctor sent us a bill saying they billed old insurance company and they were originally paid, but then the insurance company discovered the mistake and forced the doctor's office to repay. The doctor's office now wants me to pay them back because they can no longer bill the new insurance company for something so old. I told them that I provided the new insurance information, but they don't care. I also said it's pretty ridiculous to tell me this 21 months after the fact and expect me to pay.
1) Am I legally bound to pay this amount? If not,
2) Do I need to, and how, can I prove that I provided the new insurance information to the doctor's office?
3) How do I fight this?