Esa/uc migration problems

This is causing alot of distress , extremely conflicting information has been given and trying to explain and prove is the hardest part.
My partner was in support group of esa , had a wca in Dec 2013 with atos ( no longer appointed) . After this assessment was placed into support group.
I needed lots of help when my health conditioned worsened and my partner moved in with me in sept 2021. I was in receipt of esa support group and had also completed the wca. We were told to add my partner to my claim and , therefore received esa support group , severe dis premium . Now, to date , both received a managed migration to uc letter. After assistance from my daughter we completed the application.
My partner has received messages asking for fit note and jobcentre has booked him a client commitment appointment for Thursday next week.
We are trying desperately to make it clear that although my partner did not have his own actual claim at time of migration, he is on mine as a couple and we are in receipt of esa ir support group.
We are awaiting a call from ' a case manager' as to why this is all happening to us, as it was told to us that it was a very simple migration and no fit notes were needed / assessment etc.
My partner has had no break at all in entitlement to esa , just simply , went from single claim in 2021, to be added to my esa claim. Please help its causing us such awful mind trauma and sleepless nights .