Are you in the Army? If so, consult the JAG folks-they will advise you. The problem is, this can adversely affect your credit rating. If you don't care about that, just tell them to go to h---!
You may be able to get some help from your state Attorney General's office, or the Better Business Bureau. If they continue to harrass you about a
"debt" you did NOT contract for, I believe you have grounds for civil court action against both the magazine and the collection agency. If you sued and they settled, or you won your case, they would have to pay your legal fees and court costs as well as damages.