the EA account and swtor account using the same email address does not create a linkage to the account
if you login to the swtor account, on the overview screen is personal information on that is an EA account button that should give you an indication of the email address used on the linked EA account
if the account was created after June 2019 you do not have access to the linked EA account per
https://help.ea.com/en/articles/star-wars/star-wars-the-old-republic/swtor-ea-account-linked/
otherwse linking to steam and paying that way is another option
