(a) It is the duty of the representative to publish once each week for 3 successive weeks, and to mail or deliver to each creditor of the decedent whose name and post office address are known to or are reasonably ascertainable by the representative and whose claim has not been allowed or disallowed as provided in Section 18-11, a notice stating the death of the decedent, the name and address of the representative and of his attorney of record, that claims may be filed on or before the date stated in the notice, which date shall be not less than 6 months from the date of the first publication or 3 months from the date of mailing or delivery, whichever is later, and that any claim not filed on or before that date is barred.
     (b) The published notice under subsection (a) of this Section must be published in a newspaper published in the county where the estate is being administered and may be combined with any notice under Section 6-10 or subsection (b) of Section 9-5. The representative must file proof of publication with the clerk of the court.