When your 2022/23 Self Assessment was processed and child benefit declared your code for 2023/24 was updated to start collectng the child benefit charge at source for the 2023/24 tax year.
The balance from your 2022/23 Self Assessment will be collected in your 2024/25 tax code.
The child benefit coded for 2023/24 should reflect the child benefit payments you will receive from 6 April 2023 to 5 April 2024.
As the child benefit was updated in your tax code part way through the tax year then the system will work out what should have been collected from the 6 April 2023 up to now and make an adjustment in your tax code to collect this.
If you think that the amount of child benefit in your code is incorrect due to payments stopping for one child. if you contact HMRC they can check the dates are entered to show the child benefit has stopped and then amend your tax code accordingly.
You can contact HMRC at:
Income Tax: general enquiries