Cascading DropDown Lists vb.net

 I have three cascading drop down lists and the first two function properly but the 3rd dropdown lists doesnt. For instance, if i select a new value in the first drop down list, the second drop down lists resets or clears but the 3rd remains the same. Is there a solution for this? Thanks,
 
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<asp:DropDownList ID="ddlReason_For_Contact" runat="server" DataSourceID="sqlRFC" DataTextField="Reason_For_Contact" Enabled="true"

DataValueField="Reason_For_Contact" AppendDataBoundItems="true" AutoPostBack="true" SelectedValue='<%# Bind("Reason_For_Contact") %>'

 >

</asp:DropDownList>
        
 <asp:SqlDataSource ID="sqlRFC" runat="server" ConnectionString="<%$ ConnectionStrings ...