Problem to using sqlquery

ConnObj.Open()
        Dim mycommand As SqlCommand = New SqlCommand
        mycommand.Connection = ConnObj
        mycommand.CommandText = "insert into TableName" & " (branchId, productName) " & " VALUES (@branchId, @productName)"

        mycommand.Parameters.AddWithValue("@branchId", textBox1.Text)
        mycommand.Parameters.AddWithValue("@productName", textBox2.Text)
        mycommand.ExecuteNonQuery()
ConnObj.Close()

Dim myconn As New SqlConnection()
        myconn = New SqlConnection(ConnectionString)
        Dim mycom As SqlCommand = New SqlCommand()
        mycom.Connection = myconn
        myconn.Open()
        mycom.CommandText = "update TableName set productName= @productName where branchId='" + textbox1.Text + "'"
        mycom.Parameters.AddWithValue("@productName", textbox2.Text)
        mycom.ExecuteNonQuery()
        myconn.Close()

IF EXISTS(SELECT * FROM YourTable WHERE BranchId = @branchID AND  Productname = @productName)
BEGIN
    UPDATE YourTable
    SET Stock = @stock
    WHERE BranchId = @branchID AND  Productname = @productName
END
ELSE
BEGIN
    INSERT INTO YourTable
    VALUES(@branchID, @productName, @stock)
END

SqlCommand cmd = yourConnection.CreateCommand();
cmd.CommandText = queryFromAbove;
cmd.Parameters.AddWithValue("@branchID", branchid);
cmd.Parameters.AddWithValue("@productName", productName);
cmd.Parameters.AddWithValue("@stock", stock);

try
{
   if(yourConnection.State != ConnectionState.Open)
   {
        yourConnection.Open()
   } 
   cmd.ExecuteNonQuery(); 
}
catch(SqlException sqlex)
{
    //handle your sql exception here
}
catch(exception ex)
{
    //handle your other exception here
}
finally
{
    cmd.Dispose();
}