jfax efax.com They refuse to cancel a recurring subscription that I am not even sure I signed up for. Los Angeles California

There has been a recurring charge on my American Express bill for efax.com services. 

I tried to cancel the recurring charge by calling on June 28th and then having an online chat from their website on June 30th.  They refuse to cancel the charge after I give them my name, address and the last 4 digits of the credit card number. 

Representatives both times have said that the credit card is wrong, even though the charge for their services on that card is showing up every month.  Then, they make you play a guessing game about what email address you used to sign up the account.  After giving them the only 3 addresses I had over the past several years, they said those guesses were wrong. 

To tell you the truth, I can't find anything in the email account that I would have used to sign up for such a service (lorettathompson3@yahoo.com), evidencing that I signed up for a recurring fax service.