A missed call that I rang back a couple of hours later. Just a recorded message.
"Sorry, this number is not in use." It's long past the time when the regulators should clamp down hard on the phone companies issuing numbers to clearly dodgy entities. If people kept knocking on your door, then running away or refusing to tell you who they are, the police would get involved.
Not good enough. It's been going on for years and vulnerable people get conned and suffer.