CCA AT&T/Cingular collection

I had an AT&T/Cingular account that was on a two year contract. I recently found out a collection appeared on my credit from CCA as of 11/10. I declared Bankruptcy and it was discharged on 2/27/08, but was up to date on my phone, and continued to use it but it became a burden so I called AT&T and asked about my options. They asked for the BK number and I gave it to them and they said this would close the account. I am trying to remember all the details (I may have correspondence in my shred box) but I was very careful (I thought) to ensure there would be no liability left. They also decomissioned my phones at the time for future use. Should I dispute this debt? I've never been notified and it just appeared!