BR tax code on back pay from previous employer

I left my job working in a school in October due to disability and illness and received my final pay on 25th October. I have just received a payslip for backdated support staff payrise pay from April to 6th October but they have used the BR tax code and applied this at 50%! I don't understand why this has occurred as I had not even earned half my allowance when my employment ended. I am in receipt of Universal Credit (LCWRA) and PIP. What do I need to do to correct this please?

Hi,
We cannot access your personal records on the forum
If you have a personal tax account you can amend your estimated income online to update your tax code here:
Personal tax account: sign in or set up
Alternatively, you can contact HMRC to review/update here:
Income Tax: general enquiries
Thank you