Your account has been sent to studio for fixing, they should email when it is fixed
support can see you managed to sub via steam in the mean time
I tried to enter a prepaid subscription code and got the following message.
"There is an issue with your Electronic Arts account which will prevent SWTOR purchases until resolved. Please contact customer support (https://help.ea.com/en-us/help/star-wars/star-wars-the-old-republic/swtor-support) for further assistance."
I have reset my EA password several times, including using one of the links posted here. And I have used multiple browsers as well as incognito.
My SWTOR account is linked to a Steam account, and my SWTOR account name is MurlocsXD.
I also have an authenticator if that matters.
