Been battling with this issue since FIFA 19 (PS4). Bought FIFA 20 yesterday assuming it was be a bug and that it wouldn't be an issue in the new version of the game but got the exact same message with the wrong email address for the login verification.

Don't understand how there isn't just an option to manager your linked accounts in settings on your EA account!

I've filled out the online forms but will be asking for a refund myself if no response in next couple of days.

I think this Cade chap is just an automated response - customer service is dreadful...

Hope you get your issue resolved!