I agree with Mr. Doland. For your information, what the plaintiff must prove at trial, at a minimum, is that you incurred the debt, you didn't pay the debt (or at least not all of it), and that the plaintiff either was the other party or has acquired the rights of the other party. If it was a promissory note or a written agreement, the plaintiff should produce the original at trial for cancellation, or prove why the original cannot be produced. These things are not difficult for the plaintiff's attorney to do, and may be tricky for an amateur to stymie. Hence the need for a competent attorney.
Good luck to you.
I think you would be well served by a lawyer for your legal matter. Lawyers generally file a "laundry list" of affirmative defenses, some of which they prove at trial and some of which they abandon. You sound as if you might have a viable case, but even winning cases can be lost by the inexperienced.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Your desire to see the documentary proof of the debt and ownership are correct. Depending upon the amount at stake you will need to decide whether the involvement of an attorney is warranted. It can certainly help. At the end of the day, it is the creditor's burden to prove the existence of a debt and their ownership.
By responding to your question I do not intend to create, nor does it create an ongoing duty to respond to questions or an attorney-client relationship. My response is intended to be only my educated opinion and it should not be relied upon as legal advice. My response is based upon the facts provided and to the extent additional or different facts exist, my response might be different. I am an attorney is licensed to practice law only in Florida. To the extent that I am responding to a question posed by an individual in a different state, my response is being given to generally respond and the questioner is ALWAYS advised to consult a local attorney for a more specific and definitive answer to the question posed.