This article is from the Credit cards and Consumer Credit FAQ, by adams@spss.com (Steve Adams) with numerous contributions by others.
Strictly speaking, the Fair Credit Billing Act says you may not have
to pay "the remaining amount due." However, I and some other
consumers have found that our banks aren't quite so picky.
My advice (and remember I am not a lawyer) is to follow the standard
procedures for disputing a charge and simply not to bring up the
issue of whether you've already paid part or all of it. Odds are,
your bank won't raise that issue either.
However... It's best to examine bills carefully before you pay
them. If you question a charge on the 58th day, a month or more
after you've already paid it, the bank is entitled to wonder if
you're really acting "in good faith" as the law requires.
 
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