He also said they can't do anything about usage on my account, but that he'll put a note on my account not to bill for 4GB or so of extra bandwidth if use it this month. That an automated system, so claiming that $4 or whatever would involve a call to clueless customer service, who probably wouldn't understand what i'm asking anyway, taking up my time over a problem with their system. A small credit on my account would be a more practical way to manage it.
If anyone else has this problem, or has been overbilled for usage in the hour or two before their billing period ends, do make sure you call up and make them give you a credit. If enough people do it they might decide to fix their system instead.