Mysterious previous year underpayment.

My PAYE details for this tax year claim that I "did not pay enough Income Tax for a previous tax year" (around £2200) so my Personal Allowance is being reduced (by around £11,000) resulting in an adjustment to my tax code and hence around £200 less income per month. I have no idea where this underpayment comes from or even to which tax year it relates. When I check my figures for income and tax paid for 23/24 as provided in my PAYE online details they are correct. How do I query this?

Hi wodwocrow,
To review this you will need to contact HMRCIncome Tax: general enquiries.
Thank you.