I too am having this issue, I've logged into my EA account just recently and noticed a twitch handle I didn't recognise linked so immediately deleted it. 2FA now setup and all secure.
Now learning that an EA account can only ever have one twitch link in its LIFETIME. Surely there's some measure to remediate if it's potentially fradulent. I can't tell if it's an old login that I've caused (maybe the TV) or a hack but it was definitely not me.
Trying to raise a ticket is sending me round in circles. Just wanting to try the BF6 Beta, looks like I've to wait till the weekend.