After reading OPs post again. It appears thedarknesiam can't unlink the EA account from their Xbox account due to a ban on the EA account.
According to EA's troubleshooting article. Banned, suspended, or disabled EA accounts cannot be unlinked from an Xbox account.
https://help.ea.com/en/articles/ea-account/troubleshoot-ea-account-unlinking/
OP also states the EA account doesn't show any bans or suspensions in EA account history. In which case the EA employee may have misspoke about the EA account being banned or suspended. Perhaps they meant the EA account was disabled due to inactivity and you need to recover it by resetting the password.
If you reset the password and recovered the disabled EA account but still can't unlink it. This may be due to a mandatory six month wait before EA will let you unlink the EA account from your Xbox account.
Once you unlink a platform account from your EA Account and link it to a new one, you can’t unlink it again for six months.
https://help.ea.com/en/articles/ea-account/unlink-ea-account/
As you can see, linking and unlinking EA accounts comes with a bunch of restrictions in the fine print. EA doesn't make these restrictions easy to find, read, or understand. The restrictions are spread out over multiple web pages.