@PetrHipik
The linked EA/origin pitrs1992 account appears to be deactivated , you may need to open a ticket at help.ea.com to reactivate the linked ea/origin account pitrs1992
see if the below helps first
You need to reset the password on the linked EA account that account has the persona pitrs1992 (not PetrHipik your posting on now) that EA account uses a gmail email
use the following link to reset the password https://signin.ea.com/p/web2/resetPassword then login on that EA account to fix the swtor account for purchasing
for future purchases, use incognito mode on chrome initially if you purchase on swtor.com to be sure browser cache and cookies is cleared