kat,
It's probably not as simple as "DAN refused to pay for my treatment." Any responsible insurance company will perform utilization review when considering medical treatments. The litmus test as to whether to continue hyperbaric treatment for a diving injury is symptom improvement. If a diver's improvement has plateaued, i.e. the symptoms no longer improve with hyperbaric oxygen therapy, then further chamber treatment will be very unlikely to be of benefit, even if the diver has residual symptoms. Some facilities will want to continue treatment even after the diver's symptoms no longer improve, and that's typically where the conflict occurs. Unfortunately the diver is caught in the middle, and your frustration is easy to understand.
Caveat: I don't speak for DAN and I'm not certain that's what happened in your case, but if you call DAN and ask them to explain, my guess is that's what they'll tell you.
Best regards,
DDM