How do i provide feedback on representatives?

I am trying to find out how to provide my feedback on a Representative i spoke with on the phone. There are always negative feedback that are heard and was wondering why cant we provide the good as well. I can admit when i called ATT Uverse to discuss the mix up on my bill AGAIN i was not a pleasant person at all. The Representative handled it very well and by the end of the call it turned my whole day around and made me pursue trying to find out how i can help the representative. It hasn't been often for me to get a representative that listened to everything i said, repeated my issue back to me while explaining how he can help, and went as far to provide me a promotion i wasn't aware of. I now feel bad about the way i entered the call and want him to know i appreciate the way he handled my account and the real hard part me. If someone could please help me to figure out who i need to contact so L**** gets the recognition he deserves.

[edited for privacy]