There is an e-file confirmation number that you should have received when your IL was accepted. It sometimes takes a few days from the time your return was accepted before it shows up in their system. IL can take longer. Where is my IL refund? If you have the confirmation number on the acceptance report, you can rest assured that the state of IL has your tax return.
One can understand Illinois saying they haven't gotten the 2023 return if you filed near the deadline. if you called and they say they haven't gotten 2 years you need to follow up by calling them and have both year's confirmation numbers at hand and PDFs or printouts of the returns.
Also, double check the wording, to see if they might be saying that you didn't pay some taxes due to IL.
i.e. maybe they received & accepted your tax data file...but if you owed IL some more taxes to IL when you e-filed....were those taxes due actually paid to them by you.