I had a jerk online seller try to stiff me out of an order.
If they are not responding to your emails just tell them if you do not receive a credit back to your card within 72 hours you will be contacting your credit card company about the fraudulent charges and filing complaints with the Attorney General (of whatever state business works out of), the FBI cybercrimes unit at IC3.gov and the Federal Trade Commission. Worked for me, got a response within 48 hours
Unfortunately I had already re-ordered the items through another seller (amazon) and the poop head decided to just send me the merchandise instead of refunding my credit. Ugh.