SMS using gsm modem VB.NET

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VB

I am trying to write a send SMS program using SIMCOM 900A. With My below code I am facing the problems...

1.
sending when getting serialport received-data as

> AT+CMGS="9674642260"
TESTING SMS-1

It is sending the message text preceded by the entire serialport received data.

message sent : <pre>ATAT+CMGS="9674642260"
TESTING SMS-1

2.
But not sending SMS when received-data is

AT+CMGS="9674642260"
TESTING SMS-1
> 

if I click the send button again then it is sending the sms successfully but again with entire command set + message text.

can anyone help me where to modify my current code. Also I need to send the message to multiple numbers.
Thanks in Advance.

What I have tried:

my send button code:

<pre> If SerialPort1.IsOpen Then
            SerialPort1.Close()
        End If

        SerialPort1.Open()
        Try
            With SerialPort1
                .Write("AT" & vbCrLf)
                Threading.Thread.Sleep(1000)
                ' .Write("AT+COPS?" & vbCrLf)
                ' Threading.Thread.Sleep(1000)
                .Write("AT+CMGF=1" & vbCrLf)
                Threading.Thread.Sleep(1000)
                .Write("AT+CMGS=" & Chr(34) & txtNumber.Text & Chr(34) & vbCrLf)
                .Write(txtMsg.Text & Chr(26))
                Threading.Thread.Sleep(1000)
                '.Write("AT" & vbCrLf)
            End With
            rcvData.Text = recData.ToString
            SerialPort1.Close()
        Catch ex As Exception

        End Try