unknown charge debited to our account

We have an unknown charge from Comcast business debited from checking account of  $7438.14.

 I spoke with Orvil yesterday but the email address he gave me bounced back (@comcast.com) I tried xfinity.com, also bounced back, and then tried @comcast.net, which seemed to go through.

 I need quick resolution; this is a large sum to be taken without notice or documentation.