There ought to be a "emergency shutoff" threshold, period. And there's just no customer-centric excuse for not implementing it after these many years.

Here's how to implement it:

"Amazon, what do you do today if my credit card fails and all the retries fail?"

Do THAT if billing hits <my emergency off switch threshold>.

Will it disrupt the heck out of all my AWS services? Of course. That's the point, if something went so seriously wrong that my billing hits an absurd level that will put me out of business, I'd rather have downtime.