This is not really a correct statement. A public board can still have experts or people that have had direct experience with a given, specific situation as members and willing to respond. Such responses would not qualify as speculation, at least as I see it. The point is I am able to speculate and Google with the best of 'em, so I don't really need that, or advice like "just pay it...it's what I would do". I need what I don't have...an expert's viewpoint or thoughts from people who have had a similar experience.
With all due respect, experts (professionals) are not in the habit of giving 'free advice' on most forums. Some on here do provide generic information or links to IRS/HMRC information, but none are likely to 'tell you what to do'. Further, without knowing the specifics of your situation, even if someone here had a similar experience, it might not be directly applicable to you.
You have 3 choices:
1) do nothing - which hasn't made it go away, given the last correspondence from HMRC;
2) pay the bill and get on with your life;
3) or, if you think HMRC is in error, then write to them asking for specifics and provide evidence of your last filing and tax paid.
The general rule in most cases is ignore the tax man at your peril. In my first response I asked if you had contacted HMRC - and you haven't answered that question. You might be able to check your record on-line; I can, but I file a self-assessment, and I'm not sure how it works on a PAYE scheme, which I assume would have applied to you. like it or not, if you do owe the tax, then you need to pay it.