Letter asking for immediate payment - error?

I received a letter today asking for an overdue amount (Simple Assessment). The letter arrived today (16.09.24) but is dated 09.09.24. It says I owe money from 2022-2023 and need to pay or contact HMRC in next 28 days or it may be passed to debt collectors. This amount is different to what I was aware of. I usually check in on my tax affairs via logging in through the Gateway and when I just logged in, this information is different to the letter. In my logged in account it clearly states I paid the correct tax for 2022-2023 and have nothing further to pay. I do owe a smaller amount for the 2023-2024 year which I have already started to pay off online (this is all clear to see when I log in) Why is today's letter conflicting with what my account on line is telling me? Many thanks

Hi,
Unfortunately as we would need to access your records to answer your query, you will need to contact our Income Tax team for advice.
Income Tax: general enquiries 
Thank you.