You're just going to keep going round and round until you get that title. Keep in mind that the seller is under no obligation to provide a duplicate title. And neither is the state of IL.
Send a certified letter with a return receipt to the seller so you know they actually received your request. Kindly explain the situation. Make sure to offer to pay them both for the copy of the title (in WI there is a fee for a duplicate title), and their time. And don't be chintzy about your offer. $50-$100 may motivate them to help you out.
And be prepared to take some time off and make the 10 hour drive to get that title. I wish you the best on this and hope it all works out.