DukeHazzard wrote: Why can't Verizon categorically block unused numbers?

The FCC only recently gave carriers permission to do this. I'm sure it takes time to implement this.

Latest FCC Action

On Nov. 16, 2017, the FCC adopted new rules to allow voice service providers to proactively block certain types of robocalls that are likely to be fraudulent because they come from certain types of phone numbers, including those that do not or cannot make outgoing calls. For example, perpetrators have used IRS phone numbers that don't dial out to impersonate the tax agency, informing the people who answer that they are calling to collect money owed to the U.S. government. Such calls appear to be legitimate to those who receive them and can result in fraud or identity theft. Service providers now can block such calls, as well as calls from invalid numbers, like those with area codes that don't exist, from numbers that have not been assigned to a provider, and from numbers allocated to a provider but not currently in use.

Stop Unwanted Calls and Texts | Federal Communications Commission