Why your billing dates may be different from when you purchased Facebook ads
You're charged once a month on your billing date or when you reach your billing threshold, not necessarily when you purchase ads or when they run. Because of this, you may be charged after you purchase ads or even after you've stopped running them. Learn more about your billing date, how your billing threshold works and when you'll pay for your Facebook ads.
Bear in mind that you won't be charged more than the budget that you set for each ad. Remember that you're always in control of how much you spend. However, your final bill may be more than your budget for a particular ad. That's because your account is charged for all ads that you're running on it.
If you see charges that you don't think are related to your billing threshold, learn more about steps to take when you don't recognise activity on your ad account.
More billing resources
* Nguồn: Facebook