North Shore Agency Kids Discover trying to rip off my 9 year old son Westbury New York

I was given a free subscription to sign up for Kids Discovery through my childs school. After the free complimentary issue, I sent in writing that I did not wish to recieve any further issues.
About a month later I recieved a letter stating that my child owed 16.95 for the subscription. I ignored the statements and now I am recieving statements from North Shore Agency and they want me to pay the 16.95. I didn't even receive an issue!!

I have continually tried to contact these people, but it is quite convenient that there is never any phone numbers. I have sent letters and I have the receipt, I told them that, but I am still getting no response. I recieved this letter today and it said "Early Warning Notice.."
I refuse to pay this and I tried to call the number but all I am getting is a recording. How do companies get away with this and I wonder how many other families are going through this but are just paying it to not have to deal with the hassle??
I looked up North Shore to see if I could find a phone number and I can find nothing.

Kim
Sandy Lake, Pennsylvania
U.S.A.