If a merchant made a mistake on your bill and you didn't catch it within two months of its appearance on your statement, you still have an option.
Even after the 60-day window for reporting a billing error to your card issuer, you have the right to ask for a correction of a merchant billing mistake and withhold payment of the disputed amount by citing "claims and defenses," says Bowne.
To do this, you must not have paid the disputed amount, says Bowne. As long as your balance has remained higher than the disputed amount, you've preserved your rights, she says.
How to do it: Even if you speak by phone, write a letter to the merchant outlining the mistake. Include copies of anything that proves your argument and ask the retailer to correct the problem.