Here's something I just don't understand about this: How could anybody ever just "opt out" charge you money for anything? Charging somebody requires a contract

Here's something I just don't understand about this: How could anybody ever just "opt out" charge you money for anything? Charging somebody requires a contract between the two parties. That doesn't need to be written or signed, but there must be an agreement between the two parties of some sorts, verbal or whatever. If not, I could just spam the world saying "I herewith unlock you for Foo Service at $5000 per month, opt out by travelling to the North Pole and doing a waltz around it". Surely, that must be illegal in US law, too? How do these people not end up in jail? Or at least sued to death by some consumer organization?