Не выводит таблицу фильтрация LINQ Запрос C# WPF

Конструктор

<Grid>
    <StackPanel Orientation="Horizontal" Margin="4,44,4,383">
        <TextBlock Text="Код" Width="100" FontWeight="Bold" HorizontalAlignment="Left"></TextBlock>
        <TextBlock Text="Имя" Width="500" FontWeight="Bold" HorizontalAlignment="Left"></TextBlock>
        <TextBlock Text="Тариф" Width="150" FontWeight="Bold" HorizontalAlignment="Left"></TextBlock>
    </StackPanel>
    <ListView x:Name="YLV" Margin="0,72,0,41">
        <ListView.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding nomer_zapisi}"/>
                    <TextBlock Text="{Binding nomer_licevogo_scheta}"/>
                    <TextBlock Text="{Binding Mesyac}"/>
                    <TextBlock Text="{Binding Tariff}"/>
                    <TextBlock Text="{Binding kolvo_kilovatt}"/>
                </StackPanel>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
    <StackPanel Orientation="Horizontal" Grid.Row="1" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="90,17,0,5">
        <TextBlock Text="Поиск по тарифу" FontSize="14" HorizontalAlignment="Left"></TextBlock>
        <TextBox Width="150" Margin="5 0" x:Name="FiOTbx" TextChanged="FiOTbx_TextChanged"></TextBox>
        <TextBlock Text="Фильтрация по тарифу" FontSize="14" HorizontalAlignment="Left" Margin="5,0,0,0"></TextBlock>
        <ComboBox x:Name="FioFlit" Width="150" Margin="5,0,0,0" SelectionChanged="FioFlit_SelectionChanged"></ComboBox>
    </StackPanel>
    <StackPanel Orientation="Horizontal" Grid.Row="1" VerticalAlignment="Bottom" HorizontalAlignment="Center">
        <Button x:Name="BackBtn" Content="Назад" Margin="5" Height="30" Width="150" Click="BackBtn_Click"></Button>
    </StackPanel>
</Grid>

Код

    public LQY()
    {
        InitializeComponent();
        FioFlit.ItemsSource = new[] { "По умолчанию", "По возврастанию", "По убыванию" };
        FioFlit.SelectedIndex = 0;
    }
    void Update()
    {
        var ac = Connect.context.Ychetn.ToList();
        ac = ac.Where(x => x.Tariff.ToString().Contains(FioFlit.Text)).ToList();
        ac = ac.Where(x => x.Tariff.ToString().Contains(FiOTbx.Text)).ToList();
        switch (FioFlit.SelectedIndex)
        {
            case 1:
                ac = ac.OrderBy(x => x.Tariff).ToList();
                break;
        }
        if (FiOTbx != null)
        {
            ac = ac.Where(x => x.Tariff.ToString().Contains(FioFlit.SelectedIndex.ToString())).ToList();
        }

    }

    private void FioFlit_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        Update();
    }

    private void FiOTbx_TextChanged(object sender, TextChangedEventArgs e)
    {
        Update();
    }
    private void Tarif_TextChanged(object sender, TextChangedEventArgs e)
    {
        Update();
    }
    private void Name_TextChanged(object sender, TextChangedEventArgs e)
    {
        Update();
    }

    private void BackBtn_Click(object sender, RoutedEventArgs e)
    {
        Nav.MainFrame.GoBack();
    }
}