IMO this is something which ought to be written into law. It'd be easy to implement a kill switch, and would actually encourage innovation, as people would feel more empowered to experiment with the technology.
In fact, you could even just change that to any auto-billing service or product and the default for constant-charge services would simply be the amount of the constant charge.
If it's really so 'complicated' that that part can't be done, well, I'm sure it would suddenly become a business priority to cut off use when the limit is hit, if the business can't charge for it.