Does this sound OK?
RE: and Acct number here.
Dear Sir/Madam,
This account belongs to my son, HIS NAME HERE, who has not lived with me for more then a year. I have not seen or heard from him in months.
This is a request that you stop calling my home in effort to collect this debt. Any mailings from your company will be thrown away since I never see my son nor do I know his whereabouts.
I am aware of the fdcpa and will consider future contact from you as harassment.
Sincerely,