The customer service folks at any insurance organization only detail benefit coverage. They are not capable of understanding the importance of facilitating treatment with an out-of-network provider. I would contact United on Monday and ask to speak to a case manager.
Case managers are generally nurses who have the ability to look at "the big picture". They will assess, plan and facilitate quality, continuing care services while advocating for the best quality, most appropriate care for your son.
Additionally, you have the RIGHT to appeal any benefit determination that United makes regarding your son's care. Make sure to ask United for written information about making a benefit determination.
And, finally, the Patient Advocacy Foundation may be able to offer additionally suggestions on how to challenge the system. You can contact them at www.patientadvocate.org