This used to be the hardest question to answer when i used to work at Comcast and you will see why in my answer.
This charge occurs when someone is dialing 411 calls. Each time you call 411 (depending on market) is about 1.99 and to have the call completed costs 2.49. This is not a Comcast charge as a 3rd party runs 411.
i would suggest contacting Comcast billing at 1800 COMCAST as they can give you the times and dates of those calls and can possibly help you get a few of them credited.