Statement Discrepancy: Random Interest Charges on Payments on Account not Requested

I have paid my full statement amount due in January 2024 (including interest charges on payments on account I did not request as I am no longer self-employed). I now receive another statement with additional interest charges due on an apparently previously owed amount I have not seen anywhere before (I have the paper statements and screenshots of my online account statement in January to prove this). After I checking my online account just now I spot yet another discrepancy between what I owe online vs what is stated in the paper statement. Can anyone please advise on how I can receive a proper explanation for the various discrepancies and why I seem to incur charges? I have tried the phone lines and online services but with no results (Cannot get passed automated responses to a useful answer). It's beginning to feel like someone has hacked my account.

Hi,

We would need to access your record to review the statement for you.

You can contact our Self Assessment team below.

Self Assessment: general enquiries

Thank you.