Internet Order LLC Canceled account and still getting threatening letters that I owe them money philadelphia, Pennsylvania

My under age son ordered a Spanish course for $9.95; I said for this amount, he could go ahead and order it.  Shortly after we got a package in the mail stating that my credit card was charged $128.
I called and spoke with a rep to cancel my account.  I decided to keep this order as it was too inconvenient to go through the return process, and I figured that my son might be able to get use out of it.

Next thing I know, they charged another $128 so I call the credit card company and declined that payment and made sure that this company was not to be paid as I had canceled my account and no other items were received.  

Now, my underage son is getting threatening letters with supposedly his social security number on it stating that he owes $128 and that they'll give him bad credit and that it'll hurt his lifestyle.  He's 14!  He has no credit at this point in his life.  I've called and left two messages.  No one ever answers the phone, so I decided to submit this report.