Afni mistakes i've made resolving a dispute Bloomington Indiana

While trying to buy a home recently, i came across an afni collection for over 1300 dollars from cingular. this is, in no uncertain terms, not my debt. i have been a gingular (now at&t) customer for almost 10 years now, and have only ever had 1 account with them - the one i use now.

i called the call center to get information, which was an absolute waste of time, other than to start my 30 day clock running. during the course of my conversation i made sevral mistakes and would love some advice on how to make sure these things do not haunt me too much.

i verified the last 4 numbers of my social - hesitantly, but i did it.
i updated my current address.
i updated my daytime phone.

while i completely agree that these were huge mistakes, what can i do to prevent them from becoming my downfall?

Parkbc
Benbrook, Texas
U.S.A.