How to check pulse or network response using ussd at command in winform C#

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C#

WinForms

Need Help
i creating simple a Winform c# used for checking pulse in GSM Card, it uses Wavecom modem. I didn't know the code how to check or network response recieve in my winform.
Anyone can help me,.. when i insert txtUssd then press button btnCheck , the result otomaticly appear in txtMessage.

this is my form

Here The Winform Image