The account credit probably goes to the agency, and the actual customer is none the wiser. Or it gets credited to some kind of covering-our-asses fund that can be used by the agency to make the click-through cost look a little less bad at the end of the next quarter.
Which account registered the "fraudulent * " clicks? That account receives $X per click, which we've determined, and no you can't see our math. Proprietary information, don't'cha'kno.
*Advertising host admits no wrong-doing, has investigated itself, and found itself not at fault. Offer subject to limitations. See Attorney General for details.