Convert Date into dd/MM/yyyy using C# and VB.Net in ASP.Net

Hello,

I am using simple asp:calender to select date and i want date in dd/mm/yyyy format

My code :

<asp:Calendar runat="server"  ID="clinvoicedate">
    <SelectedDayStyle BackColor="#F4F4F4" ForeColor="Maroon" />
    <TodayDayStyle BackColor="#000000" ForeColor="White" />
    <OtherMonthDayStyle ForeColor="#CCCCCC" />
    <DayHeaderStyle BackColor="#E9E9E9" />
    <DayStyle BorderColor="#286090" BorderStyle="Solid" BorderWidth="2px" />
    <TitleStyle BackColor="White" ForeColor="Black" />
</asp:Calendar>

And in code behind i am trying to get dd/mm/yyyy format.

My code nehind :

string idate = DateTime.Parse(clinvoicedate.SelectedDate.ToString()).ToString("dd/mm/yyyy", CultureInfo.InvariantCulture);

but it gives format as -  dd-00-yyyy.

e.g. - if i have selected date 2 march 2018 then the result of above conversion is - 02-00-2018

where as i want it as - 02/03/2018

Thanks in advance