Natural Source Store - South Beach Smile Trial south beach brite I cancelled the order but they are still charging me. It said a free trial offer on the web page davie, Florida

I answered an add for a free trail offer in which I would receive a trail size amount of teeth whiting compound for a small fee (shipping charges under $5 bucks)...After three or four months I started receiving "DO NOT REPLY" emails stating that I was being charged $78.83 to my debit card because I didn't cancel in time????I read nothing when I ordered the product that said I would be charded this....I have called this company many times and tried to cancel the order that I never placed and never received...The company rep said he would forward my info to a third party(collections)I now see that this company has been doing this to alot of people...how can we stop them?