There are several ways to "fix" this and use VoiceAttack. First you can go into the settings menu for Elite and under Audio you'll see a plus next to one of the options (I can't remember exactly but it'll be easy to find). If you expand that you'll see the many *many* commands and their associated setting. You could either mute certain commands one by one or mute them all. I don't know that you'd want to mute them all as I'm pretty sure the game is going to say things to you without VoiceAttack initiating it. For example VoiceAttack can't say "shields off-line, taking damage" or other rather important things. So you could just start muting what you don't want in Elite.
If you don't know when you create or edit items in VA you can have it output any text you'd like by using Text To Speech (TTS). Obviously the recorded VA or Voicepack voices are going to be far superior, since they are real humans, but the TTS in Windows these days is actually rather good. I've created about 20 or so custom commands and use the TTS voice to talk back so I know it heard and executed my command. I play in VR and use Discord while I play. In conversations it's common that we'll post in-game screenshots to each other. That's sorta tough in VR as I have to take off my headset, grab my keyboard and mouse, position my headset properly (while not on my face), grab the screen shot and paste it to Discord. So instead I created "Share Screenshot" and it does all that for me automatically. I hate taking my headset off as it kills immersion so doing it this way not only keeps immersion going but it's a very slick and easy way to do it. In this example at the very end the TTS voice says "Screenshot successfully shared" (there's no logic to know it actually has been, I just know that the command has finished)
Make sense?