A few days ago I responded to an ad looking for 'home workers'

I filled in a form and paid a $0.97 shipping fee and received some useless information. Having now read the small print on the add I have noticed that they intend to charge my account by $79.90 per month. I would never have agreed to this and feel that the ad was totally misleading.

How can I cancel this and make sure that I am not billed for any money?