How do I cancel a subscription that apparently does not exist??

Somebody PLEASE help. I have found Adobe are charging my credit card monthly (£17.15). I raised an account and find no subscription purchases on there. So, I went through my ITunes account just in case I have inadvertently bought something (I have a "free" Adobe Reader on there). There is no subscription noted there either. It seems impossible to communicate directly with Adobe. How on Earth do I cancel something I have no knowledge of and no trace of ?? Has anybody else had this experience?