Home Office taken over £6K off partner claiming overpayment of wages & saying he's retired!

My partner is an employee of Home Office Border Force - ex HMRC (40 years impeccable service). A few weeks ago he received a letter from Home Office stating he had been over paid some years back. They haven't provided any evidence of this and demanded over £3000 to be paid. My partner had no choice but to pay it. Then approximately 2 weeks later they didn't pay him his wages (took another £3000 from his bank account). They claimed he'd retired in April 2024 and were taking back his Annual Hours pay etc. He is still currently employed full time with Border Force. They were very quick to take all his money, but now trying to resolve the issues, it is proving hopeless. He has wasted the last week, along with his manager to try and correct things. The staff at the end of the phone have been useless, and passing him from call to call. They've also messed up his pension. He retires in April 2025. They are saying he will get £20k less than what was calculated. What on earth is going on here? Who should he speak to? How do they expect us to survive with no money? I am absolutely furious with them! As an ex employee of HMRC myself (thank god I left) I am so shocked at the way they have treated him. He has an exemplary record, has always gone above and beyond and this is the thanks he gets. 2 questions. How does he get access to the details that show where he was supposedly overpaid? Secondly, how does he get his wages paid that they've illegally taken, given he owes nothing and it is their mistake with the retirement date? I am so disgusted with what they have done and its caused incredible stress. He is beside himself with worry.

Hi,
Unfortunately, it is not possible to check individual tax records through this forum, if you have a question which relates to your husband's personal tax situation or tax code then your husband should contact our Income Tax team.
Income Tax: general enquiries
If he has a Personal Tax Account (PTA) then within the Pay As You Earn (PAYE) section he can view past and current income with tax codes from employers and pensions.
If  neither of you have a PTA then you can set one up at:
Personal tax account: sign in or set up
Issues with overpayments of pay calculations, non payment of wages, retirement calculations should be addressed through Border Force Home Office or Civil Service Pensions. 
Thank you.