End of year tax code change not updated by employer

My tax code changed on 19 March 2024 due to me completing the form online for travel expenses. However my employer has not received it and has now processed the last pay roll for this financial year. I am due a refund of approximately £500. Will this be refunded automatically by HMRC once the tax year ends and if so when will it be refunded. How do I prevent the new tax code carrying over for next year? Thanks in advance.

Hi ML M
As soon as your repayment for 23/24 is calculated, you should be able to see it, and claim it, via your personal tax account.
Please go to:
Personal tax account: sign in or set up
You should also be able to check your tax code here.
If you need to change your code, or would like to check the progress of your repayment, contact us by webchat or phone here:
Income Tax: general enquiries
Thank you. 

In case anyone else finds themselves in this position, here is what happened. My P60 was issued but the HMRC website didn't update to show my tax had been calculated. After several attempts to get through by phone to them I did eventually managed it. The operative confirmed from my verbal figures on my P60 that an overpayment/refund was due and he agreed to do it manually. I logged on 24 hours later to claim the refund and today it is in my bank. It would have been much longer had I waited for HMRC to contact me.