Non-coded income and tax code change

I had an email today that HMRC had changed me to an emergency tax code and reduced my tax-free personal allowance. Why would they make this change when my 23/24 tax hasn't been calculated yet, of which I am confident I was over paying for. I have requested the non-coded income to be removed but still, how can my tax code be changed?

Hi,
We can only give general answers on this forum, and your question would require access to your tax record.
Please see link below for ways to contact HMRC to enable us to review the issue fully -
Income Tax: general enquiries
Thank you.