How to close UDP port?

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VB

Hi all, I programmed a network program that uses UDP protocol. The program simply send text to other program and the other program received and respond with answer.
The problem is I have multiple forms the two forms uses the same port and for that my Visual Studio give an exception that I can't use same protocol/network/ or session.
So, after I finish working with the first form close it at this event the port must closed and the second form works with the same port that opened in the first form.

' this object is thread that receives data.
    Dim t As New Threading.Thread(AddressOf ReceiveMessage)
' this function will start the listenning
    Public Function Listen(ByVal port As Integer) As Boolean
        _LPort = port
        _IsListening = True
        _Timer.Interval = 100
        _Timer.Start()
        _IPEP = New IPEndPoint(IPAddress.Any, _LPort)
        _UDPlsn = New UdpClient(_IPEP)
        done = False
        t.Start()
    End Function
' this function will stop listenning
    Public Sub StopListen()
        IsListening = False
        done = True
        t.Abort()
    End Sub
' this sub is the thread that receive messages from other program.
    Private Sub ReceiveMessage()
        Try
            Do
                _Data = _UDPlsn.Receive(_IPEP)
            Loop Until done
        Catch ex As Exception

        End Try
        Threading.Thread.CurrentThread.Abort()
    End Sub

How can I close the port in C# or VB.net ?????