dropdownlist selectedvalue doesnt change

Question

I have this dropdownlist, this one load with the data that I get from a store procedure, as you can see the load is correct, but when I change the selected value in the debug the selected value doesnt change, it stays in the first loaded value, which in this case is 1. What can I do?

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Dim adaptador As New SqlDataAdapter
    Dim datos As New DataTable
    Dim ord As SqlDataReader


    Conexiones.AbrirConexion()
    Conexiones.Cnn.Open()

    Dim cmd As SqlCommand = New SqlCommand("sp_devolver_empresas", Conexiones.Cnn)
    cmd.CommandType = CommandType.StoredProcedure

    ord = cmd.ExecuteReader

    datos.Load(ord)

    cbEmpresas.DataSource = datos
    cbEmpresas.DataTextField = "Nombre"
    cbEmpresas.DataValueField = "Identificador"
    cbEmpresas.DataBind()

    Conexiones.Cnn.Close()

End Sub