When you make a courtesy call from Notice Form (CBP Form 4333A received) from Customs and Border Protection (CBP), the entry Division in a port of entry is merely informed you that your entry has liquidated. If you liquidate an entry, this means that the record was closed. The term "entry" refers to the CBP process for importing an item in the U.S. If the courtesy notice says explicitly that additional duties are owed, this form is not requested anything from you.
Often people are not aware that they are "imported" something. If something was sent to you from another country, it is considered an import into the U.S. CBP has one year of filing the paperwork involved in a record review to determine whether all required information is completed on the paperwork, and to confirm that the rate initially correctly on the item is (for many products the tariff rate "0", so if you are not duty collected, there is no reason for concern that you owe perhaps mandatory - unless the message tells you to ) do. At any time during this year, CBP may "close" the entry, at which point you (the importer) will be sent a courtesy visit indicate notice. If you need additional information, contact the port where the entry was originally filed and ask for the entry Division. The courtesy and privacy should tell you which port your item entered by the United States.