Kindly verify few things:
From you code:
Dim enc As New System.Text.UTF8Encoding()
TextBox.Text = enc.GetString(datas)
place a line in between the two lines and see what you get:
Dim enc As New System.Text.UTF8Encoding()
System.Diagnostic.Debug.Print(datas)
TextBox.Text = enc.GetString(datas)
Also, please check
MaxLength property of your TextBox. It should not 1.
Here is a sample code for how to use GetString():
Dim datas As String = "The web page address is www.google.com"
Dim b() As Byte = Encoding.UTF8.GetBytes(datas.ToCharArray)
Dim StreamData As String = Encoding.UTF8.GetString(b)
System.Diagnostics.Debug.Print(StreamData)