I was never billed for ER visit and now it's on my Credit report.?

Two yrs ago I went to the ER, they took my information, my vital signs, i waited for a couple hrs in pain and then just left and went to a diff. ER. Anyways, they never sent me a bill. Then two yrs. later I apply for a loan and I'm refused because there is this bill. So I called the hospital and they said there is a charge whether I'm seen or not for $144. So I asked why they didn't send me a bill? She said we didn't have an address for you? Yet.. when I asked about the bill she had me confirm my address. When did they get that address? So I told her, you didn't have my address, why didn't you bill the insurance company for it? Her response was that the insurance co. wouldn't pay for a visit if I didn't see the doctor. Then I said, "so you sold to a collection agency that quickly without trying to find my address".. She said we can't afford to find people's addresses it's less expensive for us to just sell it to a collection agency.. Wow, can you believe that? How about just a quick call to the insurance company for an address? Anyways, she told me I had to contact the collection agency to get it resolved. I called them and asked them why they hadn't sent me a bill. They said they did, but it came back undeliverable. So I went to the ER in 2007, but I never received a bill from them either. The address they gave me that they sent it to was the actual hospital address.. What did they think I lived at the hospital? Well, anyways I gave them my current address to send me something? But it's on my credit report and how can I get them to take it off. I'll pay the $144, would have taken care of it 2 years ago if they had Mailed me a bill. Gee. Now I can't even get a Sallie Mae Parent plus loan to pay for my son's college expenses. For a little thing like this.. Any suggestions