incorrect P45 form

Hello, My employer sent me a wrong P45 form and refuses to send me the correct form. They also changed my tax code from 1257L to OT on my last payment without a tax notice issued by HMRC. This resulted in tax overpayment. I need the correct P45 form to get a tax refund with my next employment as well as for my Self-Assesment. What can I do to receive the correct P45 form? I already e-mailed them 6-8 times.

Hi,
Unfortunately, it is not possible to check individual tax records through this forum, if you have a question which relates to your personal tax situation or tax code please contact Income Tax team: 
Income Tax: general enquiries
Thank you.