2 Answers

Heaven help you!  Contact whoever they are and tell them you want to cancel service.  Ask them outright if you have signed a contract or if you are on a trial.  If you are having payments taken from your checking account or billed to your credit card, IMMEDIATELY contact both and do whatever you need to have that STOP.  If you have no contract, it shouldn't be impossible.  A contract you signed will haunt you for the duration.  You will likely need to put your cancellation request in writing as well.  Make sure to copy your letter AND send it RRR (return receipt requested).  

If you don't have an address or phone number for whoever, just "google" for contact information.  For example, I want to get hold of customer service for Nerds, Inc.  I would enter this for my search 

"NERDS, INC. customer service contact information"  

GOOD LUCK. 

whoops.