Paultexas

Hi All, I had my sleeve performed by a well known and respectable North Texas Clinic in June 2017. I am loving how I feel etc, and have got to my goal weight. Operation was 16 Months ago. Yesterday I received an invoice for $1782.78 for co-insurance from my anesthesiologist ( the total for 2 Anesthesiologists was $17k) I believe they were out of Network. I wouldn't mind, the surgeon only billed $3K. And why 2 Anesthesiologists when It was routine, no known prior or during issues and I was in and out in 45 minutes. I believe the Anesthesiologists were out of network. But I was not told any of this and it just doesn't seem right that 16 months on I am receiving a first invoice for such a huge amount. The co insurance I owe on 1 Anesthesiologists is $82 the other is $1,700. What advice do you have people? I don't understand insurance etc. and any advice on how to deal with this would really help. Thanks Paul