paye : incorrect information, employer marked redundancy payment as taxable

Hello, Made redundant in July this year. As par redundancy discussion I was suppose to get £23000 tax free with my last payroll. However it was taxed in payslip and marked as normal payment. On complain to HR/Finance dept of ex. employer, taxed amount was returned (£10k). Furthermore, the PAYE information listed on HMRC still shows my taxable income in tune of £50k whereas it should have been £23k less. Now my Previous employer is refusing to provide any P45 and nor amending the data with HMRC even though I have complained almost every week. Question is - How can this be corrected at HMRC paye information so that next employment or dividend payout doesn't incur higher tax. How can I file tax return next year based on my own calculations when I do not have corrected payslip or tax paid information at hand. Will HMRC accept my own numbers (£27k instead of £50k) ? What could be done to force employer quick action to sort the mess they created in July 2023? Regards, 

Hi rajesh purohit,
If the pay and tax figures submitted were incorrect then the previous employer will need to submit the amended figures to update your record.
If they have refused to do this you will need to write to HMRC with the details to review with evidence of the amended payment.
The address is Pay As You Earn and Self Assessment, HM Revenue and Customs, BX9 1AS UK.
Thank you.