Here's proof.

I have had the same experience. I changed to a new phone and number to avoid the scam calls and ATT assigned me a new number that was "dark". Now they want to charge for a new number. 

Every number is on the dark web. All that’s needed is an area code. A prefix and go fro 0000 to 9999 

Lol! You're incorrect.  If that were true my current number would be. The problem lies with more people than phone numbers. Why are we stuck at 10 digits? If we used more digits, there would be less use of the same numbers. Also, you would be the first company to do this and offer security such as not being attached to the dark web. The very first # I got from AT&T still had the previous users social media attached to it. I could sign in on his Facebook, Instagram and Twitter.  I did not do this just so you know but if that # had gotten into the wrong hands, they could have gotten access to his personal info and used it for fraud. Now I know you can't control what the user does with said # but it should be at least alarming to you that this happens on a regular basis. I have already talked with the presidents office of AT&T about this issue and apparently I'm the first to ever bring it up. That scares me. It shows that almost everyone does not know about this being a thing and that their personal info is just being given away. The pesidents office also told me there is nothing to be done. Adding more digits is a start and I'm sure there are more possibilities but if you guys aren't willing to try, than there will never be a resolution.  Why can't you at least try??

@vernonhc they have waved both charges for me when I brought up the issue. If they don't for you than that shows how much they do not care. Ive only been a customer for 3 months and have had to change 2 numbers already. I am sorry it happened to you as well and I'm worried for everyone else. This is bigger than you and I and it affects everyone who has ever used AT&T or any carrier in that matter. This is our life's they have control over and something really needs to be done about it. Oh, please go through everything you used the old number they gave you and remove it from everything because whoever gets it after you can access your info if they use the same site or anything you've used that number to sign in on or attached to a 2 way security process. 

What makes you think your numbers have been on the "dark web?" What do you think someone can do with your phone number? They used to pass out books to every household listing the phone number of the entire community. How could you sign into social media accounts using just a phone number? Even if that's someone's sign-in ID, you would have to know their password. 

If there's been a data breech somewhere, your phone number is probably the least useful item of PII they could get. 

@BDay15  AT&T, or any provider can't just add extra digits to their phone numbers. That would be an FCC thing and probably other governmental agencies so it's not gonna happen. People who purchase or provide info on the dark web are usually very sophisticated in how they use and manipulate that info. If you've ever purchased a home, a car, or anything, and had to supply your phone number, email address, home address, ad naseum your info has been collated, packaged, and sold on the dark web. 

Unfortunately there is very little that any provider can do about the dark web. And once your info is there, it's there forever in some form or another.

MicCheck, to answer your ignorant question "how do we know number is on the dark WEB I have a service from Experian credit bureau that sends notices when there are threats to my credit rating. A phone number helps the scammers gather more info until they get enough to be a problem. I told the salespeople that I was changing my number because it is on the dark web and getting a new phone. They had no reason to believe the new number was corrupt but ATT should have known before they "sold" to me!  

Welcome to AT&T's ignorance of customers' problems. There is plenty of information about phone numbers, including what is directly reported by customers at https://www.att.com/support/pages/report-call-or-text . At a very minimum, AT&T could just quickly check via "algorithms" at e.g. https://www.shouldianswer.com/ or even Experian. But that's just really hard for a big company of talented employees. Instead, ACEs here will be arguing and nitpicking about irrelevant things.