FWIW:
I work for AT&T in a supervisory role (not getting more specific than that for obvious reasons) and if there's one thing that upsets all of us, it's people that come in/call just asking for fees to be waived for no real reason other than being cheap and acting entitled. If you're cool about it or it wasn't explained to you or something, we'll probably make the adjustment. If you act like an entitled snob and disrespect us, you'll not get very far.
This isn't even an AT&T thing, really. It's customer service and, hell, people in general. When it comes down to it, you signed a contract agreeing to pay the $18, and by no means are we required to waive it.
tl;dr like the adage goes, treat others the way you want to be treated.
As a side-note, there's no way our agents are allowed to suspend accounts or send out abusive text messages like that EVER. I can guarantee you that if that rep's supervisor found out about it, she's gone.