If the patient is under the care of another provider, who also treated the patient on the same day as your provider, for the same medical condition, there isn't much chance of winning an appeal. You might want to find out if this other doctor was part of the care team for the patient or was he a doctor trolling for patients.

This happened to me while I was in the hospital. I was under the care of Dr. X for a diabetic episode. I just received a bill for $700 for one day of care. The bill came from Dr. Y. Dr. Y says he was in the hospital and came to see me on that day, yet I have no record of him seeing me. You see, I kept a small book during my stay and I recorded every doctor that came to see me and when. Dr. Y is of the same specialty as Dr. X and Dr. Y says he saw me for the same medical condition as Dr. X. I asked Dr. X if he called in a consultant and he said he didn't. I then sent Dr. Y a demand for the medical record and the referral/consultation documents.