Unless notice has already been given under this section, a personal representative upon appointment may publish a notice to creditors whose identities are not reasonably ascertainable. The notice must be published once a week for three successive weeks in a newspaper of general circulation in the county. If the personal representative elects to publish a notice to creditors then, in addition to publishing the notice to creditors, the personal representative shall mail a copy of the notice to those creditors whose identities are known to the personal representative or are reasonably ascertainable and who have not already filed a claim. The notice must announce the personal representative’s appointment and address and notify creditors of the estate to present their claims within three months after the date of the first publication or mailing of the notice or be forever barred. For the purpose of this section, a reasonably ascertainable creditor includes a creditor who regularly submits billings to the decedent or the decedent’s estate and to whose billings the personal representative has had access.