You should contact your credit card or debit card issuer immediately and report the issue.  By law, consumer liability for debit and credit card charges is limited to $50 when fraud is reported.  However, VISA and MasterCard, who control 100 percent of the U.S. debit card market and the majority of the credit card market, have gone one step further and require that all of their credit card issuers (like Capital One, Chase, Citibank, etc.) adhere to a zero percent liability policy for their customers.  They also require that immediate refunds be granted on disputed charges.  Most other major credit card networks have applied these rules as well.

This means that you should be able to get your money back right away, including over draft fees that were the result of the disputed charge.  If the merchant admits to an error after your bank has investigated the matter, that will certainly make things easier.