35 ILCS 120/6c
If a protest to the Department's Notice of Tentative Determination of Claim is not filed within 60 days and a request for a hearing thereon is not made as provided in Section 6b of this Act, the said Notice shall thereupon become and operate as a Final Determination; and, if the Department's Notice of Tentative Determination, upon becoming a Final Determination, indicates no amount due to the claimant, or, upon issuance of a credit memorandum or refund for the amount, if any, found by the Department to be due, the claim in all its aspects shall be closed and no longer open to protest, hearing, judicial review, or by any other proceeding or action whatever, either before the Department or in any court of this State. Claims for credit or refund hereunder must be filed with and initially determined by the Department, the remedy herein provided being exclusive; and no court shall have jurisdiction to determine the merits of any claim except upon review as provided herein.
35 ILCS 120/6c