If it were me, I would call Tricare first to see if they have any record of payment or denial of claims during the time frame you're talking about. You should be able to give them that info based on the dates listed on your credit report. That will be MUCH easier than trying to get a hospital billing dept. to give you info from 4 years ago. You may be able to get the answers you need from Tricare that other moms have mentioned here (did they pay anything, is the amount you owed the amount they didn't cover, etc.). Here's the contact info page from the Tricare website:
http://www.tricare.mil/contacts/
Regardless of which Tricare plan you have, the contact info should be listed there. We still have Prime, and we have 100% coverage, even if we are seen in an ER (Tricare no longer does pre-approval for ER visits, they just tell you to go to your local ER. We have done this numerous times w/our kids over the past 5 years).
Once you know what you're dealing with regarding Tricare's payment obligations, then you can contact the credit agencies to clear up the listing on your credit report if it was made in error. If it wasn't, then you should be able to work out a payment plan with the collection agency representing the hospital. If it is in collections, I'm surprised you haven't been contacted by the collection agency, especially after this amount of time. Those things usually go into collections pretty quickly, so maybe the credit report issue is a mistake. If it is, you can submit a request online to each of the 3 credit bureaus to correct it. Good luck with it all!