g.zod; that link is so full of twisted logic, I think the wroter must have been a pretzel maker at some time. They say one thing and then provide case law seemingly to support what they said. The problem is, it often support it in the manner they implied it would.
This is the controlling law.. Validation is a simple procedure which the collector simply contacts the original debtor to verify the debt. That is it. You do not have a right to demand an accounting of the account. No payment history, no contract showing this agency has the right to collect the debt. Those are all things you can demand in court but there is no requirement to provide them before.
Of course, when the debt went in to default is critical, if you want to argue an SoL defense so figure that out and when you do, then you can go to the next step.
You are being sued so you need to do things quickly. Your time is limited.
if any advice given my divemedic or ashman get you off, please let me know but generally, they are giving you false hope.

