If it is about the change of your username, theymos can do it but he has done it for only well established members before. Members that are having low rank may not be able to have that benefit. But even if you will have the benefit, it may take time. I remember how it took people like The Sceptical Chymist a very long time before theymos changed his username. But my advice is that you should not have such in mind until you ranked up more and become well established.

In my experience: theymos probably reads it and responds when it's needed, but PMs are often ignored. So if you didn't get a reply, you can assume you're being ignored on purpose.
Judging by your topic history: if this is related to PMs you sent, I don't think Admin is going to help you as that would mean censoring PMs received by others.