AT&T cancellation glitch

In December of 2007 I thought I cancelled my contract with ATT Mobility, as we got very poor coverage in our local area. I asked to port my husband's business number to our new carrier, Alltel. Even though I asked what to do if Alltel was unable to port the number, I was never told I needed to call and cancel that line. Alltel was unable to port the number and it is evidently left open and I was charged two months of service on that account as well as the $175.00 buy out fee. In talking with their customer service people I was told it was my responsibility to learn what to do to change carriers and not their responsibility to tell us (me).