The issue isn't the time that has passed, but where the purchase was made. Consumers can dispute the quality of goods and services for purchases made by a credit card in your home state or within 100 miles of your current billing address under the Fair Credit Billing Act, or FCBA. That's the bare minimum. Some issuers will expand those dollar and distance limits; others won't.
Those restrictions also don't apply if the merchant is the credit card company, or if the merchant and card company have a special business relationship. I'm not sure if that's the case here.
The act also stipulates that the purchase exceed $50 and that the consumer make a good-faith effort to resolve the issue with the merchant first, which sounds like you've already done.
If this had been a billing error rather than a complaint about the purchase, you would have had 60 days after the purchase first appeared on your credit card statement to dispute the purchase with your credit card company under the FCBA. The company then would have conducted an investigation and responded to you within the 30 days required by federal law.
The "mail or telephone order merchandise rule" -- which covers online purchases -- also doesn't apply in your situation because that rule only deals with the timely delivery of purchases.
Here's your last resort. Check with your state laws for purchase protections. You can take the same legal actions against the credit card issuer as you can take against the merchant under state laws. Otherwise, you're out $6,000.
In the future, stick with well-known, reputable online merchants. If the merchant is unknown to you, read customer reviews and check with the Better Business Bureau and state attorney general's office for recent complaints before placing an order. Keep track of order documents, including ads or Web pages advertising the merchandise. Also, know the company's return and refund policy. Unfortunately, it's "buyer beware" when it comes to online shopping.
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To ask a question of the Credit Card Adviser, go to the "Ask the Experts" page and select "Credit Cards." Read more columns by the Credit Card Adviser. Follow Janna Herron on Twitter.