I bought a single 6 month membership to OkCupid today, or so I thought. The website rejected my billing information for my debit card twice before I narrowed down the problem to a wrong zip code and my purchase was finally accepted. Turns out that they had charged me 3x, even though their website claimed my account wasn't charged for my previous attempts. I contacted OkCupid through their support box, but they just cancelled my subscription and did not email me at all or respond to my refund requests. What should I do next?
Since you just made the purchase today, the transactions you saw on your account are pending transactions. After a few days, transactions get finalized/cleared/posted, but often the transactions change when they go from pending to posted.
It is possible that if you hadn't called and they hadn't cancelled your account, two of the pending transactions would have disappeared and only one would have remained on your account.
Now that they have actually cancelled your account, it is possible that all three transactions will disappear in a few days.
It is also possible that you have been overcharged, but it is too early to tell. You generally aren't allowed to dispute a pending transaction for this very reason: it isn't final, and is subject to change.
What you need to do is wait a few days. Hopefully, your bank's website gives some indication which transactions are pending and which are posted, and after the transactions have switched to posted, you can see what you were actually charged, and either contact OkCupid again or dispute the charge(s) with your bank.
Unfortunately, with a debit card (as opposed to a credit card), pending transactions get deducted from your balance immediately, and often there isn't a good indication on the bank's website of what is pending and what is posted. If you can't tell by looking at your transactions which are pending and which are posted, you'll just need to wait a few days before you can assume that they are finalized, and go from there.