According to a thread in Digital Point Forum, Google Adwords account can never be canceled!
"I have discovered to my dismay, that Google does not permit an Adwords user to permanently close his account once it has been activated. Your account is not canceled but only deactivated. It can easily be re-activated with a simple click of the Reactivation link provided."
This has gone to such severe lengths that the same AdWords advertiser has chosen to cancel his credit card. "So much for canceling your Google Adwords account. I suppose I have no choice but to cancel the credit card I used for this account- to assure Google will not have access to my financial information- and move on."
As autocratic as this is many support the move, even saying "From Google's point of view, they don't want people closing accounts, then starting new ones without it relating back to what happened in their old account. Look at the number of posts in this forum that claim the way to solve a problem in an account is close it and start a new one."
Personally, I am all for closing the account, but who knows what you feel. Meanwhile, discussion continues at Digital Point.