Let's see. $600 minus the $7 connection fee equals $593 or 53 minutes at $11/minute. That must have been some conversation. You can dispute the bill with the credit reporting companies certainly and the phone sex company cannot bring charges themselves, only the DA can. I doubt a DA would charge you under these circumstances. You have learned a valuable lesson in dealing with businesses that offer unconventional services. If you have evidence that the charge was supposed to be $2.99/hr I would calculate the 53 minutes at that rate and pay them although they probably can't enforce their contract anyway.
Dispute the matter by going to you credit card company. On the back of the card is a customer service telephone number for you to phone. Lay out the detail of your situation and keep a record. All papers that you have relating to this should be saved.