My wife recently has surgery that was approved by Blue Shield prior to the procedure. Now Blue Shield says they may not pay?

My wife had surgery in June that was pre-approved by Blue Shield. They now tell me they are conducting an investagation into this as to whether or not she was eligible for the surgery? The cost of the procedure was $70k! The surgeon has now indicated she needs further surgery as she could have a condition that could be life threatening if the second procedure is not completed. Please advise as I am in a dilemma as to how to proceed.

Thank You