i sympathize with you. First off I am not an attorney. I can only tell you what I read.
I would start by visiting the courthouse (clerk of courts) get copies of everything.
then you need to prove you were a resident of another state. Contact utilities and
anyone that can provide proof of your residence in illinois.
Now the tough part. You need to go to a website that can provide you some assistance in filing paperwork to reopen the case based on not being served properly
I can suggest one site. But ripoffreport.com will censor the name I give. So the name is Debtorboards. Put it together and you have it.
I have visited this site for help. they have attorneys that will unoffically help you.
Its a maze. but you need to reopen the case and prove they did this. Now, my suggestion is that if you get the judgment vacated take it to jury trial. This will
really get unifund in a frinzy. Hire a NACA lawyer. They love suing Unifund. Right now they have a class action suit against them. This like the third one they had in 10 years. sometimes they will take it on contingency fee.
I wish you the best.