You are right to be concerned about LVNV! This happens alot. Here is a link to a debt validation letter at
http://www.debtconsolidationcare.com.../about216.html you can tweak it to fit your needs.
Make a copy of all correspondence-yours and theirs. Make notes of when you talked with them,dates and times- you may need this later.
Send all your correspondence certified, return receipt at the post office. It costs more, but you will have proof they received it.
LVNV doesn't validate-or they haven't mine. The next step would be to write them and tell them to cease and desist from contacting you, if you know this is not your debt.
If you need more help, feel free to ask questions..KAren