815 ILCS 205/4.2a
If a lender or creditor, within 30 days from receiving a written letter, in clear and definitive terms, signed by the debtor, including his or her name, address, and account number, sent within 60 days after mailing by the lender or creditor of the statement on which the alleged error first appears, concerning an alleged error in a revolving credit account fails to answer the specific question concerning such error in clear and definitive terms, for that 30 day period and for any further period that the lender fails to provide a clear and definitive answer, the debtor shall not be required to pay any service charge on the disputed amount.
A lender or creditor who complies with the federal Truth in Lending Act, amendments thereto, and any regulations issued or which may be issued thereunder, shall be deemed to be in compliance with this Section.
815 ILCS 205/4.2a