I would just dispute the charge with the credit card company. They hate "chargebacks" and will quickly put the screws to vendors who are causing problems. Terms like this are more than likely against the merchant agreement the vendor has to sign to accept a brand of credit card.
In general you have to dispute the charges within 60 days (beware any offer that encourages you to try it out for more than 60 even if they promise a full refund).
There are consumer protections and rights that can't be set aside by store policy or terms and conditions but the credit card companies are usually even more pro-consumer in this instance (might seem out of character, but the CC have a vested interest in you feeling safe to purchase cruft. Merchants are really the ones over the barrel in this relationship) than is required by the law.
In general, their behavior is probably all bluster trying to bluff you into rolling over or getting some amount of money. It's doubtful that they even have a membership with a credit reporting agency to even make a report--that's why it's important to be preemptive with your card issuer.