Thanks!
Second, Google will continue to try to charge your credit card.
As in other businesses, if the bill is not paid by credit card, other means will be found to get you to pay, which may include selling the bill to a collection agency.
I suggest you contact Google ASAP to try to work this out. If you give them a good reason why the billw as racked up so high, they may be willing to work with you on the issue. However, since you received the reward (increased traffic to your site), unless the mistake was on Google's side, I doubt they will forgive much of the bill.
Google has several functions in place to prevent people from accidentally blowing their budget (daily caps, etc.). So failing to use them properly isn't going to be much of an excuse.