Error 54002

I'm trying to buy a subscription, but i'm getting this error '54002'. I've searched for info and some online users said that to solve the problem I need to remove my EA saved payments info. But the problem is that I never used EA(ea.com) to buy anything. I've always used swtor.com to buy my subscription. Is there a way to solve this?

Another question is: I've downloaded my game from swtor.com, is it okay for me to buy the subscription from Steam? Or it'll cause an error?