Medical bill - Am I liable for attorney's fees without notice?

(Indiana)

I received ONE medical bill dated December 17 for $850 balance due after insurance had made their payment, but I didn't received the bill until sometime in January, don't recall approximate date -- didn't think it was a big deal at the time (the printed invoice had the address area whited out and hand-written in -- assume they had a wrong address and it had been returned). I sent the doctor a check for payment in full February 8. I received a letter from an attorney the end of that week demanding payment plus $250 in attorneys fees. I called the attorney the next day and explained the check had already been sent to the doctor before I received their letter. The doctor received my check and the attorneys are still demanding payment for the $250 plus interest. I only received one invoice, never anything else from the doctor, such as a notice or indication that it was going to collections. There was no contact from the doctor except the initial invoice. Can I be required to pay the attorneys fees? Where can I find information to dispute this unfair act?