Illinois doesn't have any way to check that someone isn't cheating on their taxes beyond using the addresses that taxpayers are using. You didn't do anything wrong but until you prove that to them they have no way to know.
You can try filing an Illinois non-resident return showing zero income along with copies of your federal and state returns for the year in question. Include a cover letter explaining your situation along with a copy of the letter that you received from Illinois. Mail all of that to the Illinois department of revenue at the address shown on the letter that you received.
@d3904887
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
