By now there is a default day (2nd day of each month) where DO try to bill on credit card. But this date is not the best for all customers. Me, as a example, only pay my credit card on the 10th of each month. That being said, each month I see DO trying to bill it (and failing) until day 10.
There should be an option for you to set a day for billing, or at least letting you choose between "start" or "end" of the month.
This way I don't look like a "swindler" or something and don't feel bad with the daily "Failed to pay" e-mails.