This is just an update on my previous post for anyone with the same issue.
Someone in another forum said they received the same letter from ESA after migrating to UC. They had to repay overpayments of ESA as IR ESA did not stop. UC took back the overpayments from their UC.
They had to call ESA to tell them the date they migrated, as ESA did not know. They said it was sorted out on the phone. I hate calling DWP but looks like I'll have to call ESA Ion Tues morning if I can get through..
