In general, I would say the best way is to e-mail the diamond desk. This way you have a written record of what the complaint was and a time stamp of when it was submitted. Given that you've already submitted a written complaint, heard nothing and the issue has not been resolved, I would call the diamond desk. I have found them to be exceptionally responsive, especially when I call and tell them I had submitted a complaint via the website or e-mail that was not addressed.