Try this (assuming the problem is in this part of your code)
Directory.CreateDirectory(textbox1.Text);
File.Move(filetran, textbox1.Text);
You should note that:
1. Directory.CreateDirectory() causes no complications if the directory already exists.
2. Path.Combine() takes either an array or more than one argument.
3. Your previous code was doing nothing as you had a '!' before your condition, thus the code only acted if the directory did not exist.