Bear in mind, I am just a volunteer here:

First off, I would immediately call your credit card company, explain the situation and ask if they can remove the charge. (While you are at it, ask for a new card with new number).

If they can't remove the charge, call Comcast. Again, explain the situation.

If that doesn't work, I would go talk to the police and ask if there is anything that can be done.

Wish I could be more helpful on this.