ESA payback overpayment - follow up

Sooo after 15 months my husband received a letter on 17/12/2022 they posted 2/2/2022 (do they not know RM is on strike)!
With 5 days notice the fraud squad is going to take from his state pension £246 for the next 3 months. And more. The debt is £1026.
I have in writing that they were aware of him declaring his works pension. He had sent in pay slips etc at that time and he would never of hidden that fact. First time ever on the sick aged 64. Had the fraud squad telephone interview (this was lockdown times). I wrote in within 5 days on 20/9/2021 to Debt Management Wolverhampton, and not heard a thing since. I asked if they could look at the decision again before I appeal. I assumed it must have been dropped as my benefit was instantly reduced (ESA new style). 15 months and now this letter. I never got the chance to appeal or even know where to appeal. And I became a pensioner in April this year and ESA stopped. In all I was on ESA from May 2020 until April 2022.
I don't think he should be paying this back. It was all their fault. Today I contacted the DWP Debt people and reduced the payment to a bare minimum with the hope that I can get the chance to appeal or at least object to what has gone on.
Any advice, much appreciated.
Thanks

ESA New style for one year then ESA support group one year. Been to citizens advice not helpful! Phoned debt collector other day, reduced payment to the minimum. Then phoned ESA who said nothing on system since I wrote to them Sept 2021. ESA now looking into it and have to give a call within 3 days. They have phoned today and we unable to to take call. I will follow this between hospital appointments next couple of days. Will let you know outcome. Thanks