You should cut right to the offender. Whoever is the one reporting on your credit report...LVNV is KNOWN to play musical collectors and will happily shove an account all over the place in an effort to frustrate your right to validation. Attack the one doing the reporting, since by law they can't just 'close' the account without also closing out the account on the credit report.
Also if you get a collection letter from someone claiming to collect for another company, if that company is NOT the original creditor, then send THAT company your validation request. You then send a letter to the contacting company that you have send their client a debt validation letter and are informing them of same, that the debt in question is now under validation and no continued collection activity may take place until the validation request is satisfied.