call the better business bureau!
i've been on-line shopping for years and have had very good luck but i am very careful about where i shop- and it has to be an actual-verifiable shop with a history (as in been in business for a number of years- have links of customer comments= have a good customer service link===
can you stop your payment? if you used a credit card you should be able to contact the card company and get the charge reversed- and report the problem-
if you used a debit card i would get to the bank! make sure they did not take more than they should have and fill out the forms to reverse the transaction.
until you are familiar with a shop you might want to come here and ask...before placing an order...just to make sure it's a legitimate place- there are (crooks) all over unfortunately.