Either you did not correctly assign the event to the appropriate command, or you did not set up VC to work properly with XBMC. There is a tutorial video that shows you exactly what you need to do.
Also there are a number of ways to perform a soft mute. Unless you can give us some way to know what you are actually doing, I'm not sure how we can help.
Did you ever read the forum rules? There is a link in my signature which appears on every message I post. There are some important guidelines and suggestions there on how to create a support request in an effective way. This is a valuable skill that once learned, will help you to seek help more effectively on any forum.