It's a nightmare sometimes to cancel credit cards, especially if you're travelling.

There are some banks that simply won't cancel the card until you visit your local branch. A tricky maneuver when it's 2000 miles away (I don't know if they've changed this now). Likewise, there are things that are hard to find if you use your cards a lot and don't keep detailed receipts on everything you buy. This happened to me when I discovered someone's been deducting a small sum from my card for several months without me noticing as I was overseas. Of course they could only take care of the last charge before cancelling my card.