I was called by this number (314 621 2430) and I called it back. It says this number is not in service.

I was called by this number and did not answer.  The man left a message saying that he was giving me a courtesy call and if I was making minimum payments (assuming credit cards) then calling him back would be a good opportunity but that I had to call him back the same day. At first, I panicked, thought maybe I missed a payment on a store credit card so I went into my accounts to make sure that I was not behind.  I listened to the message again and realized that he wasn't call to collect money. I always pay more than the minimum on my credit cards so I'm not sure why this guy was calling me and how he got my cell phone number. The number he gave me to call him back at was 866-237-7637.  When I search that number on this site, it appears that many people are receiving the same calls and are putting this guy on a "do not call" list.

the number calls but when I dial it back it says it's not a working number.

Missed call from 314-621-2430. Dialed back, it rings in, but says it's a non working number. ???

He just called me too. After introducing myself, there was a man who said "Err...Hi?" and was then silent for while, before finally hanging up.