First things first! Don't let these bottom feeders get to you. They know they are in the wrong, but will hound you and try to harass you in attempt to scare you into paying.
Under the law, you have 30 Days from receipt of Written notification either ask them IN WRITING to validate the debt, or make a payment if you know the debt to be valid if you fail to respond in any manner. After that thirty days they will assume the debt is valid. You can still ask for validation. BY law within 5 days of the first contact you should have received a written dunning notice from SAM (however I am certain you didn't). That's your first FCRA violation ($1000 should you try to pursue that).
If they fail to produce validation of the debt , they can no longer collect on it (however they will refuse and continue to try to collect) after about 4 months they will send your account off either to another agency or an attorney. Their attorney's (Arthur Corrales, Ft. Walton Beach, FL or William D. Smith, Atlanta (suburb), GA) also will refuse to produce validation, however they will comply with the fdcpa.
In the case of Mr. Corrales, I asked for validation, he did not respond and two months later I got a call from Mr. Smiths office. (at the time he contacted me he was not registered with either the Georgia or Illinois Bar Associations. He is Now registered with the Georgia State Bar after I called him out on this). He will attempt to validate, though his documentation was incomplete. HE WILL ATTEMPT TO DOCUMNET YOU MAKING COMMITMENT YOU DID NOT. You must correct this in Writing as soon as you become aware.
In my case I asked for validation and 6 months later I received incomplete documentation, however in an effort to resolve the matter I offered a payment plan which he has not yet to respond to (9 months later). Hope this helps some what . fee free to PM me if you have any questions.