If they are a corporation you might want to check with your Secretary of State website to see if they are registered as a corporation & obtain information accordingly. I presume WI has that reuirement, but I am not sure since I am a California attorney.
This is not intended to be legal advise or as legal representation. I am a California personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters.
Why not just call the Wis DFI: Office Hours: 7:45 am - 4:30 pm
Telephone: (608) 261-9555. They can probably tell you.