35 ILCS 630/10
If it shall appear that an amount of tax or penalty or interest has been paid in error hereunder to the Department by a taxpayer, as distinguished from the retailer, whether such amount be paid through a mistake of fact or an error of law, such taxpayer may file a claim for credit or refund with the Department. If it shall appear that an amount of tax or penalty or interest has been paid in error to the Department hereunder by a retailer who is required or authorized to collect and remit the tax imposed by this Article, whether such amount be paid through a mistake of fact or an error of law, such retailer may file a claim for credit or refund with the Department, provided that no credit or refund shall be allowed for any amount paid by any such retailer unless it shall appear that he bore the burden of such amount and did not shift the burden thereof to anyone else, or unless it shall appear that he or she or his or her legal representative has unconditionally repaid such amount to his customer (1) who bore the burden thereof and has not shifted such burden directly or indirectly in any manner whatsoever; or (2) who, if he or she shifted such burden, has repaid unconditionally such amount to his or her own customer; and (3) who is not entitled to receive any reimbursement therefor from any other source than from his retailer, nor to be relieved of such burden in any other manner whatsoever.
If it is determined that the Department should issue a credit or refund under this Article, the Department may first apply the amount thereof against any amount of tax or penalty or interest due hereunder from the person entitled to such credit or refund. For this purpose, if proceedings are pending to determine whether or not any tax or penalty or interest is due under this Article from such person, the Department may withhold issuance of the credit or refund pending the final disposition of such proceedings and may apply such credit or refund against any amount found to be due to the Department as a result of such proceedings. The balance, if any, of the credit or refund shall be issued to the person entitled thereto.
If no tax or penalty or interest is due and no proceeding is pending to determine whether such person is indebted to the Department for tax or penalty or interest, the credit memorandum or refund shall be issued to the claimant; or (in the case of a credit memorandum) the credit memorandum may be assigned and set over by the lawful holder thereof, subject to reasonable rules of the Department, to any other person who is subject to this Article, and the amount thereof shall be applied by the Department against any tax or penalty or interest due or to become due under this Article from such assignee.
As to any claim for credit or refund filed with the Department on or after each January 1 and July 1, no amounts erroneously paid more than three years prior to such January 1 and July 1, respectively, shall be credited or refunded, except that if both the Department and the taxpayer have agreed to an extension of time to issue a notice of tax liability under this Act, the claim may be filed at any time prior to the expiration of the period agreed upon. Notwithstanding any other provision of this Act to the contrary, for any period included in a claim for credit or refund for which the statute of limitations for issuing a notice of tax liability under this Act will expire less than 6 months after the date a taxpayer files the claim for credit or refund, the statute of limitations is automatically extended for 6 months from the date it would have otherwise expired.
Claims for credit or refund shall be filed upon forms provided by the Department. As soon as practicable after any claim for credit or refund is filed, the Department shall examine the same and determine the amount of credit or refund to which the claimant is entitled and shall notify the claimant of such determination, which amount shall be prima facie correct.
A claim for credit or refund shall be considered to have been filed with the Department on the date upon which it is received by the Department. Upon receipt of any claim for credit or refund filed under this Article, any officer or employee of the Department, authorized in writing by the Director of Revenue to acknowledge receipt of such claims on behalf of the Department, shall execute on behalf of the Department, and shall deliver or mail to the claimant or his duly authorized agent, a written receipt, acknowledging that the claim has been filed with the Department, describing the claim in sufficient detail to identify it and stating the date upon which the claim was received by the Department. Such written receipt shall be prima facie evidence that the Department received the claim described in such receipt and shall be prima facie evidence of the date when such claim was received by the Department. In the absence of such a written receipt, the records of the Department as to when the claim was received by the Department, or as to whether or not the claim was received at all by the Department, shall be deemed to be prima facie correct upon these questions in the event of any dispute between the claimant (or his or her legal representative) and the Department concerning these questions.
Any credit or refund that is allowed under this Article shall bear interest at the rate and in the manner specified in the Uniform Penalty and Interest Act.
In case the Department determines that the claimant is entitled to a refund, such refund shall be made only from such appropriation as may be available for that purpose. If it appears unlikely that the amount appropriated would permit everyone having a claim allowed during the period covered by such appropriation to elect to receive a cash refund, the Department by rule or regulation shall provide for the payment of refunds in hardship cases and shall define what types of cases qualify as hardship cases.
If a retailer who has failed to pay tax on gross charges for telecommunications is required by the Department to pay such tax, such retailer, without filing any formal claim with the Department, shall be allowed to take credit against such tax liability to the extent, if any, to which such retailer has paid the tax to its vendor of the telecommunications which such retailer purchased and used for resale, and no penalty or interest shall be charged to such retailer on the amount of such credit. However, when such credit is allowed to the retailer by the Department, the vendor is precluded from refunding any of the tax to the retailer and filing a claim for credit or refund with respect thereto with the Department. The provisions of this Section added by this amendatory Act of 1988 shall be applied retroactively, regardless of the date of the transaction.
35 ILCS 630/10