This New York Times article, “Learning How to Fight the Collector,” describes former collection agent Steven Katz, who created a message board, DebtorBoards dot com, teaching people how to sue in small claims court, collections agencies going after them. Its members sued their creditors for over $700,000 and defended collection of over $600,000 in debts, a net swing of $1.3 million. Sadly, that message board no longer exists, and DebtorBoards dot com now belongs to a collections agency.
However, the internet wayback machine has the full archive of the message board available. You cannot log into the message board, but you can review all the posts, especially the pinned posts. The posts are intentionally very how-to/DIY. I suggest starting with “The Flyingifr [founder’s username] Method of Aggressive Credit Repair.”
Here’s a shortened link to the archive: https://is.gd/Eb6IcV
Here’s the full link to the archive: https://web.archive.org/web/20180826182027/http://www.debtorboards.com/index.php?PHPSESSID=rsltvcg02ggj9notp45j7satc5;wwwRedirect
If you’re suing, I suggest reviewing your case with your local bar association’s Ask-A-Lawyer event in advance.