Denied service due to 14-year-old past due balance

So this may take a while to explain and I hope I can do it clearly.

First, let me get the basics out of the way. I am 35, 77032, currently with BCBS, though at the time of the issue at hand I had Cigna.

Kelsey-Seybold is a network of clinics in my area. I have been there many many times though huge gaps may be in between appointments for one reason or another. About a month ago I set up an appointment for a physical exam. Today I went into my online account to make sure I had the date correct and to fill out any forms that were needed. It was no longer showing me my appointment or allowing me to create a new one. I called their tech support thinking maybe there was something wrong with their website. From there they advised me that there was a note on my account that I needed to speak with the business center.

So speaking with the business center they tell me that I have been blocked from making appointments due to a past-due balance($495). On my end on my account, it shows that I owe nothing. It shows my past appointments from 2016-2017 which is the last time I used their clinics. The agent advised me that it was from visits in 2009 and that they would send me a statement through my online account to view.

Looking over the statement it appears that out of the 4 visits listed only one of them was not paid in full. Here is a screenshot of the portion that appears to be sent to collections It was for what appears to be an annual physical. None of the tests were paid for. One thing to note is that in 2009 I was in a completely different situation than I am now. I was still under my dad’s insurance policy. I had no idea this bill even existed. It’s so far back that I don’t even remember the appointment, though I’m sure I probably had one.

Now the issue is that Kelsey-Seybold is saying that I cannot see a doctor in their clinic unless I pay the past due amount to the collection agency. I don’t believe I should owe that amount and that the insurance should have paid it. I at least want some sort of explanation from the insurance as to why it wasn’t covered. How would I go about tackling this issue? Do I reach out the Kelsy again and ask them to resubmit my information to an insurance company I’m no longer even with? Do I reach out to the collection agency and ask them to do it? Or do I somehow contact my previous insurance company at the time and try to get them to figure it out?

I really would like to go back to this clinic as they have a wide network of providers and they have excellent care but I’m debating if it’s even worth the hassle. Do I just let it sit in collections forever? I just don’t understand how if this is from 2009 it’s just now getting back to me. Any help would be appreciated as this is something that seems so daunting to me. I don’t know where to start. Also, please let me know if there is any other information that is needed.

Thank you!