I am inserting data in ASP .NET grid on rowcommand event it is inserting data but when I am refreshing page using f5 same record get inserted again

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ASP

I am inserting data in asp .net grid on RowCommand event it is inserting data but when I am refreshing page using f5 or(selecting url and then press enter)  same record get inserted again

What I have tried:

I have Asp Grid view as follows

<asp:GridView ID="GridViewRow" runat="server" AutoGenerateColumns="False" BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px" 
            CellPadding="3" DataKeyNames="Id" GridLines="Vertical" ShowFooter="true"
            OnRowCommand="GridViewRow_RowCommand" OnRowEditing="GridViewRow_RowEditing" OnRowCancelingEdit="GridViewRow_RowCancelingEdit" 
            OnRowUpdating="GridViewRow_RowUpdating" OnRowDeleting="GridViewRow_RowDeleting">
            <AlternatingRowStyle BackColor="#DCDCDC" />
            <Columns>
                <asp:TemplateField HeaderText="Id" InsertVisible="False" SortExpression="Id">
                    <EditItemTemplate>
                        <asp:Label ID="lblId" runat="server" Text='<%# Eval("Id") %>'></asp:Label>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="Label1" runat="server" Text='<%# Bind("Id") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>

                <asp:TemplateField HeaderText="FirstName" SortExpression="FirstName">
                    <EditItemTemplate>
                        <asp:TextBox ID="txtFirstName" runat="server" Text='<%# Bind("FirstName") %>'></asp:TextBox>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="lblFirstName" runat="server" Text='<%# Bind("FirstName") %>'></asp:Label>
                    </ItemTemplate>
                    <FooterTemplate>
                        <asp:TextBox ID="txtFirstNameFooter" runat="server"></asp:TextBox>
                    </FooterTemplate>
                </asp:TemplateField>
                
                <asp:TemplateField HeaderText="LastName" SortExpression="LastName">
                    <EditItemTemplate>
                        <asp:TextBox ID="txtLastName" runat="server" Text='<%# Bind("LastName") %>'></asp:TextBox>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="lblLastName" runat="server" Text='<%# Bind("LastName") %>'></asp:Label>
                    </ItemTemplate>
                    <FooterTemplate>
                        <asp:TextBox runat="server" ID="txtLastNameFooter"></asp:TextBox>
                    </FooterTemplate>
                </asp:TemplateField>

                <asp:TemplateField HeaderText="Contact" SortExpression="Contact">
                    <EditItemTemplate>
                        <asp:TextBox ID="txtContact" runat="server" Text='<%# Bind("Contact") %>'></asp:TextBox>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="lblContact" runat="server" Text='<%# Bind("Contact") %>'></asp:Label>
                    </ItemTemplate>
                    <FooterTemplate>
                        <asp:TextBox ID="txtContactFooter" runat="server"></asp:TextBox>
                    </FooterTemplate>
                </asp:TemplateField>

                <asp:TemplateField>
                    <ItemTemplate>
                        <asp:Button ID="btnEdit" runat="server" Text="Edit" CommandName="Edit"/>
                        <asp:Button ID="btnDelete" runat="server" Text="Delete" CommandName="Delete"/>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:Button ID="btnUpdate" runat="server" Text="Update" CommandName="Update" />
                        <asp:Button ID="btnCancel" runat="server" Text="Cancel" CommandName="Cancel"/>
                    </EditItemTemplate>
                    <FooterTemplate>
                        <asp:Button ID="btnAddNew" runat="server" CommandName="AddNew" Text="Add New"/>
                    </FooterTemplate>
                </asp:TemplateField>

            </Columns>
            

        </asp:GridView>

in footeer template I have button to insert data

<FooterTemplate>
                       <asp:Button ID="btnAddNew" runat="server" CommandName="AddNew" Text="Add New"/>
                   </FooterTemplate>

When I inserting Add New button It is inserting text box data into Database
but when i refresh after inserting (suppose i am pressing f5 then It is again inserting same data)

button insert code is as follows (written on

RowCommand

event) in which i have checkd command name as

if (e.CommandName.Equals("AddNew"))

entire code to insert data into grid view as follows

protected void GridViewRow_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            try
            {
                if (e.CommandName.Equals("AddNew"))
                {
                    using (SqlConnection con = new SqlConnection(strConStr))
                    {
                        SqlCommand cmd = new SqlCommand("SP_InsertPhoneBook", con);
                        cmd.CommandType = CommandType.StoredProcedure;
                        cmd.Parameters.AddWithValue("@FirstName", (GridViewRow.FooterRow.FindControl("txtFirstNameFooter") as TextBox).Text.Trim());
                        cmd.Parameters.AddWithValue("@LastName", (GridViewRow.FooterRow.FindControl("txtLastNameFooter") as TextBox).Text.Trim());
                        cmd.Parameters.AddWithValue("@Contact", (GridViewRow.FooterRow.FindControl("txtContactFooter") as TextBox).Text.Trim());
                        cmd.Parameters.AddWithValue("@Email", (GridViewRow.FooterRow.FindControl("txtEmailFooter") as TextBox).Text.Trim());
                        con.Open();
                        cmd.ExecuteNonQuery();

                    }
                }
            }
            catch (Exception ex)
            {

                string str=ex.Message.ToString();
            }
            finally
            {
                populateGrid();
            }
        }

but when I refreshing page using f5 after inserting record then

GridViewRow_RowCommand

even is firing and it is inserting what ever i have insert previous data

how I can prevent this