Confusion over income for TC purposes

Very confusing over the income taken into account for TC purposes. Claimed CTC amd WTC until it ended in August 2023 (change of circumstances child went to uni, employment details were always the same). No further payments after Aug 2023. But HMRC have taken ALL my income into account from September 23 (when I started a new job) to April 24 and say there's now an overpayment? How is that possible when I wasn't even receiving any TC from Aug 2023 onwards? The TC I received up to Aug 23 were based on the correct circumstances of my usual job and child being at home.

Hi,
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