This message means that your PlayStation account is already linked to an EA account. If you ever played any of the EA games on that PlayStation account, there is a high chance that it was linked to an EA account in order to gain access to online services. Please keep in mind that EA account and PlayStation account can have different login credentials. To activate the account, you will have to try and remember the email address of the EA account and reset password on it. You can also try and reach out to customer support, they might be able to assist with locating the correct account.