Read all the sticky threads at the top of the forum.
Go over your reports and check for any inaccuracies.
Then find out your SOL -
Check for DOFD, DOLA on your account listings on your CR. It may say something like "this account scheduled to remain until XXXXX"
It may be easier for you to work on the accounts one at a time.
If the OC has sold the account, they should report a $0 balance.
For unpaid debts with a CA, you would want to DV first, then offer PFD. However, you want to step lightly if you are within SOL. This means they can still sue and win. So, if within SOL and you want to take action on the account, make sure you can PIF right away if they were to file suit.
After doing the above, post back any questions you may have.
Good luck, it is a long road(for most) but well worth it and very rewarding when you reach the end.