Look at the terms of service you had with them and see their stated cancellation policy. Follow their stipulated policy to get your refund. If they don't comply with their own policy, and you can't negotiate anything with them but you paid by debit or credit card, talk to your card carrier, which you want to do anyway to report the unauthorized charge, and ask them to initiate a chargeback.
If your card carrier or bank won't cooperate, you can report them to the Better Business Bureau and to your attorney general's office. You can also report them to the FTC.
Finally, you can sue them in small claims court for their breach of contract.
All of this presupposes that the company is legitimate. If they are scammers, you're not going to be able to find them and it will be a job for law enforcment. Then you'd report the fraud to your police and to the FBI at their Internet Crime Complaint Center at IC3.gov. In that way, even if the police can't find them, as the victim of a crime, you'd be able to deduct your unreimbursed losses when you file your 2016 taxes.
If you reply to me here on this question thread and give the website for the company, I can look into them and determine whether they are likely to be a scam or not.