Even if you take great care to properly close your Netflix account, it is possible that Netflix may still try to hit you with additional charges after your subscription has ended. Netflix could make claims of an improperly closed account, missing DVDs, missed deadlines, etc. If this happens, you have the right to dispute the bogus charges with your credit card company, and, if you are a customer in good standing, there is a decent chance your credit card company could side with you.
You do not have to wait for a problem to occur to take action, however. If you are concerned that Netflix could hit you with bogus credit card charges after you close your Netflix account, you might consider being proactive and contacting your credit card company before you close your Netflix account. You can notify your credit card company of the date you plan to close your Netflix account and the date after which Netflix should not be billing your card. You could still get hit with additional charges, but you may then have a stronger case if you need to dispute any suspicious charges from Netflix.