Android Question Add Variable to a String

lbl_chamaIMEI.Tag = "lbl_chamaIMEI"
TextWriter1.Initialize (File.OpenOutput (File.DirDefaultExternal,$"${lbl_chamaMEI.Tag}.txt"$ , False))

Sub BtnGeraInv_Click
     
                  Dim lbl_chamaIMEI As Label
                               
         Qry="SELECT CODBARRAS,QUANTIDADE FROM PRODUTOS ORDER BY CODBARRAS"
         Cursor1=SQL.ExecQuery(Qry)
         If Cursor1.RowCount=0 Then
         Cursor1.Close
         Return
End If

            Lbl_IMEI.Text = GetDeviceId
           
            lbl_chamaIMEI = Lbl_IMEI.Text
       
            lbl_chamaIMEI.Tag = "lbl_chamaIMEI"
           
            ERROR IN THIS LINE --->TextWriter1.Initialize (File.OpenOutput (File.DirDefaultExternal,$"${lbl_chamaMEI.Tag}.txt"$ , False))
            ERROR MESSAGE ---> Undeclared variable 'lbl_chamamei' is used before it was assigned any value.

   For i = 0 To Cursor1.RowCount-1
   Cursor1.Position=i
   CODBARRAS= Cursor1.GetString("CODBARRAS") 
   QUANTIDADE = Cursor1.GetString("QUANTIDADE") 
   
   TextWriter1.Write(CODBARRAS & "," & QUANTIDADE & Chr(13) & Chr(10))
   
    
Next
TextWriter1.Flush
TextWriter1.Close
Cursor1.Close
Msgbox("Inventário Gerado com Sucesso !!","Coletor de Dados MPC®")

   
End Sub

 lbl_chamaIMEI = Lbl_IMEI.Text