I can understand how important the billing on an account is. When an account in Constant Contact is created, the account's billing currency is selected for you based on your location. However, this currency can only be changed while an account is in trial. Once an account is no longer in a trial and a payment has been made, the currency cannot be changed. I apologize for any inconvenience this may cause! Being able to update the billing currency on a paid account is a great feature request I have tracked in your account in the meantime.