Get copies of the SPD, the Plan, and all amendments. Plan language should control, but If SPD appears to give benefits not allowed by the Plan, Bene has an excellent Estoppel argument. Some reserve complete discretion to themselves.
Some plans explicitly exclude such treatments.
If this is unambiguous, and there was adequate notice, the patient probably has no recourse. Government or church employers. The Administrative Appeal. Must exhaust administrative remedies before filing suit. May file for emergency relief while appeal pending if necessary.