Medical payments..who has to pay?

My ex has custody of our child and she has a medical problem that will continue to bring in serious medical bills. I have 100% medical insurance with my job and she is covered. My ex has all the info that he needs so that the hospital can bill the right insurance company, but he puts my insurance company but his name on the paperwork when she is admitted to the hospital. This in turn cause my insurance company to deny the payment to the hospital. Am I responsible for this?..Should I call the accounting department everytime (so far 7 times) to make sure they have the correct information for billing? He says that he is going to put her on his insurance and that I will be required to pay for it..Is this true? We now live in Utah and I am unsure of the rules.
Heartbroke and worried

[This message has been edited by corky (edited June 23, 2000).]