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You're not likely to get anywhere with a first line TU csr, no. What you may be able to do is report your issue via that phone csr requesting escalation (since they can't see report with the TU New Account Score/reasons you have a copy of). I really have no idea, to be honest. @FinStar ???
Re: your orthodontist...if your relationship with the office personnel is such that you would be comfortable doing so, I would certainly request a copy of the report they were provided. I wouldn't mention the possible "impropriety". I'd just tell them it just isn't showing on your TU credit report at all, and TU can't tell you anything either. Then based on what their copy of that requested report says, you'll at least know if there is or isn't actually a reported derogatory public record of collection. If there is, hopefully it will be identified and if valid, will assuage your curiosity.
TU does thing like this and you get nowhere trying to fix it. It's a waste of time. When I pull my TU report from the Annual Credit Report site, there is a 3rd party suplemental category that states that my report was requested in 2018 by an apartment complex and goes on to say that I had a foreclosure. That is false. I was in a midlle of one when I filled BK7 in Feb of 2012. Eventhough the BK is long gone from all 3 reports, TU continues reporting this. Their agent swear it's not there but every report I have pulled it's under 3rd party additional info.
Since there's a typo in your reason codes ("of" for "or") and you've never had a collection, I suspect that the reason codes on this form are manually entered and that when your form was generated they either didn't clear the codes from the previous customer or typed in the wrong codes for you.