^ durr, you mean on the 16th of every month. such as January 16th, February 16th, etc.
After your year has expired, your monthly expenses will accumulate until billing. For instance, if in one month you accumulate $5 in charges, you won't be billed that month. But if in the next you use another $5, then your total is $10 (ie: over $9.23), and then on the 16th of that month you'll be billed.
$9.23 is a rather odd amount, but I imagine that it's how they have integrated pay-per-usage services into their system. I'm willing to bet that if you continue to make all of your payments on-time, that number will grow.
In any case, payment shouldn't be an issue. You should receive an email once billed, and should be given a period (usually 1-2 weeks) before the payment is due. The purpose of scheduling it on the 16th is because that was when you opened the account, and it's used to keep track of the bandwidth you use. In other words, for the 1800+ GB of bandwidth you have, the meter gets reset on the 16th of every month. Not a big deal if you're not using it all, but if for instance you hosted lots of big files to share, it might make sense to post/share a new file on the 16th of the month, rather than the day before, so that you aren't charged for extra bandwidth.