Re: Billing problem
If you're trying to make a manual payment, the system will usually suggest an amount based on your spend history, but you usually also get an option to choose an amount that you would like to credit to the account. If you get to that section and then proceed through the next steps (adding in the amount, checking it's correct, and confirming the payment) you should be able to complete the payment.
The only thing you can't change is the currency of the account.
Hope this helps. If you need any more help, please feel free to reply here and clarify your question.