Banned for TOS Violation: Multiple Payment Methods

I am a paying Origin Access member who recently started playing SWTOR.

After a few days enjoying the game I decided to subscribe to SWTOR. I went to the payment methods and my credit card information had automatically been propagated from (I assume) my Origin Account - I didn't need to fill anything in. I hit the button to subscribe but received an error, something was wrong with my card. So I checked my bank and there was no charge applied and plenty enough money. A little strange, but it's the internet so whatever, and I tried again to subscribe but, again, the payment was rejected.

After browsing online I found out I could buy a subscription through Amazon. So I proceeded to do this, using the same credit card which pays for Origin Access but was declined by SWTOR. No problem, Amazon is happy to take my money. After the subscription code was approved I applied it to my SWTOR account and continued to play as a subscriber. All good!

Until a few days later when I received notification I was banned for a ToS violation.

I replied to the email asking for some more information.

Today I received the following reply:

Thank you for contacting us regarding the closure of your account. The sanction on your account pertains to the following violation:

Multiple Payment Methods

Having completed a thorough investigation into your account and the complaint that you have made, we must advise that your account was sanctioned correctly, in full compliance with our policies and procedures. Following our review into the actions taken on your account we wish to confirm that we shall not be removing this ban from your account.

I've searched the ToS documents and online and I can't find out anything about what this actually means. I'm unsure how Multiple Payment Methods could be an offense so bad that I would have my account completely closed literally a few days after paying for a subscription.

I intend to contact customer service tonight. Unfortunately I'm currently on a business trip in China so it means staying up late at night and making an expensive internation mobile phone call.

I was wondering if anyone can give me any insight into what this ban is really for, what "Multiple Payment Methods" refers too, and why I would be banned from SWTOR for paying for a subscription?

I'm incredibly confused and disappointed at this point.