Where in the terms of service or in the admin UI do you see this information? You can pre-pay, yes, and the CDN service (and ONLY the CDN service) has a setting to stop the billing. But the other services do not seem to have a limit on how much you can get billed.
I don't have a credit card on file, I'm not sure how they are going get paid if my balance goes negative.
Also: https://support.bunny.net/hc/en-us/articles/360000235911-How...
But yes, other services will run until your account is dry, then it gets suspended. You can't set a spend limit on your scripts without it taking down the whole account. You can't do cost optimization, but at least you are protected from going bankrupt.