My employer keeps sending in incorrect information to HMRC

My employer initially made a mistake and did not pay me in the period before the tax year when my PAYE income would have not been taxable - because I only earned 6,000 that year. However, this tax year they keep ending my employment sending me (and you) a P45. Because I have a pension of 4,000 I am being taxed on my wages at Basic rate. I have no continuity of employment so I am constantly taxed on an emergency basis. They are a major public body and blame it on a computer glitch. I am on a zero hours contract but I am doing work each month for now and the forseeable future and my manager has intervened to try and stop them constantly ending my employment. No one else in my team gets this happening to them despite being employed on a similar basis. This has happened for the last three months. How can I get them to treat me fairly and how can I get back the tax I am paying that I should not be paying. Its about 400.00 now.

Hi sevif,
We may be able to amend your code to repay you tax overpaid so far.
To allow us to do this, and potentially advise you further on your issue with your employer, we would need to access your record - contact us by webchat or phone via Self Assessment: general enquiries.
Thank you.