update: I won this case.
I've received a judgement in the mail today, letting me know that i've won the case!!!
(I've gone for the hearing, but the plaintiff didn't show up with a valid reason - sick. I've raised some more defenses in the court, so the plaintiff had 10 days to respond.)
Below is the judgement letter:
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The defendant has raised the defense of a failure to bring the action within 5 years as required by statute.
The Court finds that this is an open and credit arrangement as defined in Iowa Code 537, 1301. The Court further finds that there is a five year statute of limitation applicable to this case, and the last date on this account was February 1999. This case is therefore dismissed for failure to file within the statutory period.
The Court further notes that the Bill of Sale provides no clear assignment of this case to the plaintiff.
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Thank you guys so much for helping me!!