Cannot remove/login to icloud on ipad after email address change
We changed the email address of an Apple ID a while ago.
The ipad originally couldn't login anymore, but with login in with the new email address and password (although the old one was displayed) at least booting worked.
Now it still keeps asking for the iCloud password. Here I cannot change the email address.
I created a new Apple ID with the old email address, but I cannot change/remove the icloud with the password I used with that one.
What can I do to fix this?
iPad Air 2 Wi-Fi