I was getting spammed to bejeesus and back from these numbers myself. I think this must be a collections agency, because when they call, they're very informal, such as sounding like they've known you your whole life and saying things like "Hey man! Is Marco there?" trying to sound like a friend or something.
So I found this site, and I went to Nuvell.com. They have a "contact us" link, you click that and you can get their 1-800 customer service number. I called there and after getting thru the voice prompts, I was able to speak with a live person. I explained my situation, that I was getting spammed with calls from two numbers apparently linked to their company, the 501-821-8252 and the 904-486-1141. I told her they I've answered and told them they had the wrong number, that my name is NOT MARCO etc and so forth. She apologized for the confusion and said she was adding a note to their files to the effect that their customer's number had changed, and she said it would take a night to "download" into all their offices, but that the calls should stop by tomorrow.
We'll see. If not I'm not even bothering with AT&T. I'm calling the authorities, as this has got to qualify as Harassment since I've taken all options I can think of to stop the calls.
Caller called two days in a row. First day, I picked up and they said that some lady left this number with them as a business contact. When I told the man noone was here by that name he wanted to know my name and I hung up on him.
Second call was answered by answering machine and they hung up and did not leave a message.