Details of Unearned Income for Tax Calculation

HMRC send me a summary stating that I owe tax on unearned income but do not provide the details of where the earned income calculation come from. Why are these details not provided within the request for payment so that they can be verified?

Hi,
We would need to access your record to check on what the unearned income relates to.
If you do not have any unearned income this can be updated.
You can contact HMRC at:
Income Tax: general enquiries