Question about divorce and insurance.?

So ok...last year I received a notice of a preliminary hearing on my divorce. It was set for Aug. 7th. I waived my appearance, and thought nothing of it. I never received any paperwork after the fact, but having had dealt with his lawyers previously on his custody issues did not think anything of the slow down (actually assumed he did not pay so they stopped work).

I was using his insurance through the military, and mine was secondary on post. In november I had an expensive procedure done that was pre-approved.

come feb. I finally asked about the divorce situation for tax purposes and was informed that the divorce was actually final aug. 8th and I should have received the paperwork, which I did not.

Now a year later, after he produced the divorce papers to get his new wife on his tri-care they are wanting to bill me for this procedure...over 3 thou.

I have the phone bill from when I called the court house where we were divorced in Feb, and emails from that time giving my friend the info to go and get the documents from the court house for me. All of this to support my claims of not knowing at the time of the bill that I would be respnosible for it.

Do you think I have an appeal? Is there anything I can do?