How to call a Function with a RETURN NUMBER

Forgive my lack of knowledge . I'm trying to call an insert function from sqlnavigator. I'm able to capture the prm1.Value, but I'm not sure how I'm supposed to include RETURN NUMBER (see SQL below) from my package spec in sqlnavigator. When I run it, nothing is added to ORACLE.

 Public Shared Function INSERT_CATEGORY()

    Dim cmdOraCommand As New OracleCommand

    Try
        cmdOraCommand.CommandType = CommandType.StoredProcedure
        cmdOraCommand.CommandText = "SF_ALEX_TEST.insertCategory"

        Dim prm1 As OracleParameter = cmdOraCommand.Parameters.Add( _ 
            "inCategory", OracleType.VarChar)
        prm1.Direction = ParameterDirection.Input
        prm1.Value = strCategory

    Catch ex As Exception
        MsgBox(ex.Message)

    Finally
        cmdOraCommand.Dispose()
    End Try

End Function

SQL/ORACLE

FUNCTION insertCategory(inCategory IN VARCHAR2) RETURN NUMBER

IS
    vReturnedValue NUMBER;
    vID NUMBER;
    vExist NUMBER;
BEGIN
    IF inCategory IS NULL THEN

        vReturnedValue := 0;
        RETURN vReturnedValue;
    ELSE

        BEGIN
            SELECT COUNT(MNT_CATEGORY) INTO vExist
            FROM MNT_CATEGORIES
            WHERE MNT_CATEGORIES.MNT_CATEGORY = upper(inCategory);
        END;

        IF vExist = 0 THEN
            BEGIN
                SELECT SEQ_MNT_LOG.NEXTVAL INTO vID FROM DUAL;

                INSERT INTO MNT_CATEGORIES(MNT_CATEGORY_ID, MNT_CATEGORY)
                VALUES (vID, UPPER(inCategory));
                COMMIT;

                vReturnedValue := vID;
                RETURN vReturnedValue;

                EXCEPTION
                WHEN OTHERS THEN
                    vReturnedValue := SQLCODE;
                    RETURN vReturnedValue;
            END;

        ELSE

            vReturnedValue := vExist * -1;
            RETURN vReturnedValue;
        END IF;
    END IF;
END;