Custody/credit issue

My ex-wife has full custody of my daughter. Recently she took her to a doctor that was in my "network". The ex did not pay the bill and now they (a very persistant collection agency) are after me for the full amount. I had no idea the bill even existed. Can I be held legally responsible for this debt?

[tbyte]

According to your court orders, who is responsible for medical bills?
I would assume you are responsible for half of any medical expenses over a base annual amount (typically about $50).
I'd say your two options are:
A) Pay the bill, keep a record of the payment, and settle up medical costs between you at the end of the year.
B) Inform the collection agency that the mother is legally responsible for paying the bills, and fax them copies of the court orders.