My employer seems to have made a mistake when totalling the income tax on my 22-23 payslips and ultimately my P60 - I have found the month where this occurred, where the year to date tax column was not updated by the full amount of tax paid that month - this was then carried forward onto every subsequent month and onto my P60 at the end of the year. Now HMRC are asking me to pay this discrepancy.
I initially asked my employer if they could resolve the issue but they said I needed to contact HMRC. HMRC have told me it's up to my employer. Who's right and is there something I can say to them e.g. a form I need to ask for, that will send them in the right direction to helping me?