Insurance Not Paying Portion of Medical Bill

yes, the doctors are both considered "In Network"

Is the 2nd surgeon billing you for the whole amount of the bill or for the portion the insurance would be paying? And have you received your explanation of benefits from your insurance company for this claim. Is there an amount in the patient responsibility section? If 2nd surgeon is indeed contracted they should also be working with the insurance company to get the claim resolved since they have a contract with them.

If both of your surgeons were in network, then chances are good that they accept assignment on insurance benefits. That means that they have a contract with the insurance companies which states that they are legally NOT allowed to bill you for the balance between what they charge and what the insurance pays. You are only responsible for your copay. This holds true even when the insurance company pays nothing, which is frequently the case for surgical assists. There is a very good chance that the bill has come to you in error and you aren't responsible. Have you gotten an EOB from the insurance company regarding the charges? If not, you need to call them first thing in the morning and ask them what they traditionally do with surgical assists. Almost every surgeon has one, and insurance almost never pays for them. It's really, really bad form that you're getting billed for this. 

 The same thing happened to me...talked to the Insurance company and they ended up paying it.