While the existing billing alert sends out an email whenever the set limit has reached, I'm not always at my inbox refreshing to get new emails and if I do, my emails usually drown each other out.

To solve this, I suggest that an automatic spending limit cutoff be implemented. Users can set a limit like we do now, and when it is near the limit like say $5, a reminder email would be sent out reminding the user that the droplets that are on the account will be frozen if the spending exceeds the limit. If the spending does exceed the limit, the droplets will immediately be frozen and the user would have to increase the limit or wait until the next billing month.