They do have a billing check, but that check is looking at "eventually consistent" billing data which could have arbitrary delays or be checked out-of-order compared to how it occurred IRL. This is a strategy that's typically fine when the margin of over-billing is small, maybe 1% or less. I take it from your description that the actual over-billing is more like dozens of dollars, potentially more than single-digit percentages on top of the subscription price. Here's hoping they tighten up metering <> billing.