Pulse of Truth

I believe the telcos themselves are the ones sharing this information with banks and identity providers. They know who you are (if you're not using burner phones), and are offering ways to use the phone number to authenticate users (in the US, don't think you could do that in a country with privacy laws).

Can't access redit through my VPN, so f-k them.

My guess is that this is to flag scammers that are using old leaked data. They might have one of your old phone numbers from one of the thousands of other leaks, and they'll choose the number they recognize that is old and invalid. Then they know the attempt isn't legit, and shuts it down.