RAXE500 -- can't sign up for Parental Controls (invalid currency type), can't switch accounts

On my main account, every time I try to sign up for a service (SPC, Armor), the system throws an error, telling me:

New plan does not have a rate schedule with a currency matching the account's currency.

I thought maybe my account was referencing an old address somewhere I couldn't see, so I unregistered the device and made a new account, then registered the router to that one. It doesn't seem to have worked -- every time I try to do something on the router, I'm told that it is already registered to my old account.

I've been working on this for days now -- phone support could not figure out the currency issue, and emails have gone unanswered.

I really need parental controls up and running. Right now I'm stuck, and getting ready to go shopping...