This actually may be legit.  I had an issue with a feature on my AT&T Wireless account, which I worked with several of their CSRs for a couple of hours without resolution.

According to the voice-mail they just left, this is their Customer Service Quality Assurance calling me back to discuss the (negative) feedback I gave them on the survey I took after the incident was closed.

this number isn't at&t don't know who it was There Normal Business Hours are from 8-5 CST M-F

It was AT&T, They call me back from this number after I hung up on them!