Send them a DV letter. Per the FDCPA, the CA has an unlimited amount of time to verify the debt and they can continue to report during that time. The 30 day period is a common misconception. However, per the FDCPA, you have 30 days from the date of their dunning letter to send a DV. Maybe they'll stop the process and verify first.
Are you inside of the SOL? You'd want to check that first. As you experienced, never touch an unpaid debt if SOL hasn't expired.
Is this for an OC account? If so, then I probably would just pay it without a PFD and then GW later. But again, check your SOL. If outside SOL, then I'd answer anything from the court and would tell the attorney to go pound sand.