I did a DV as well and got the "more information" letter as well. It's a bunch of BS, I don't have to provide any info to them to validate. I filed a FTC complaint online and sent AFNI another letter with a copy to FTC. If they can't validate, they can't pursue debt collection, reporting it to CRA's constitutes a debt collection activity.
If I don't get a response, I'm going the BBB and their state attorney general, and continue to follow up with FTC. I'll look into small claims as well. I got NCO to delete, I'm not paying AFNI one red cent.