I bought a bunch of refurbished/renewed iPads for my business and 7 of them were EUICC locked to AT&T. You could put any physical SIM in the iPad and it would work but it would not let you use a non-AT&T eSIM. AT&T refused to talk to me unless I had an account with them, I did, and then told me those iPads were not in their system, there was nothing they could do, and I should see about returning them and getting new/replacement ones.
I spent multiple hours on the phone and on their support forums and got nowhere (over the span of 2-3+ weeks). Finally I filed an FCC complaint and the issue was fully resolved in 3 days.
FCC/CFPB complaints are great tools to use and I recommend reaching for them sooner rather than later. I have examples of being jerked around by companies for a period of weeks or longer and then the issue being fully resolved in a matter of days after filing a complaint. It's my new "complain on twitter to get better/faster service".