On my summons was attached a sworn affidavit from an employee of midland Funding LLC. She swears that she has "personal knowledge of all relevant financial information concerning my account." What would be the best way to go about negating this? Shouldn't I as defendant have an opportunity to question this person?
Procedures for dealing with such an affidavit will vary from place to place. Typically though you must do something other than merely answer the complaint with one or more key denials (no denials at all results in "judgment on the pleadings") or summary judgment may be available to the other side.
What are the "facts" in your case? The facts are the plaintiff's affidavit. If you don't have an affidavit too, then the set of facts for the judge to look at will just be the ones that the plaintiff provided. It's at this point that the tiny percentage of pro se people getting sued who actually appeared and answered lose at summary judgment.