Incorrect payment regarding past salary

I have endeavoured to approach my past employer about an error made in a salary paid to me. They have already provided information but this does not answer my query and I believe they still owe me some salary for the tax years 2022/2023 and 2023/2024. I also believe they utilised the incorrect tax code. My past employers (a Parish Council) have informed me (quote): "All matters of employment have been settled and no further communication will be acknowledged in this matter." QUESTION: Please let me know if my employers can say this as I am endeavouring to sort out my tax affairs and without this information I cannot make progress. Is there a legal obligation for them to provide such information. If so, what is the regulation?

Hi Lynne,
We can check the tax code used by your employer in the years affected, and confirm if this was correct -
Contact us by webchat or phone via Income Tax: general enquiries.
Thank you.