I suggest you wait for the bill and once you get it.
File a complaint with the FTC here
File a Complaint with the FTC | Consumer Information
Then contact your state attorney general thru email explaining the situation and give them phone numbers and addresses for contact.
The cooling off rule probably wont apply for you so you should get the ball rolling early by filling a compliant at your local county attorney office for small claims court and charge them with unauthorized billing.
Keep hard copies of everything you will be asked to present them in court.
Chances are they wont even show up but if they do there is a good chance you will lose and again you could win depends on the judge, but you will win either way because you have taken part of their day away and they made no money sitting in court, no interest can be charged, no fees can be levied, nothing but the bill will be considered while in the court system.