That's unfortunately the reason you don't get the choice dialog, because LG or your service provider locked down VoiceMate. There are some locked apps on my Samsung phone too, but by luck it's not SVoice here. If you have root access, you can still delete these locked system apps from the /system/app folder. I did that to many Samsung cr@p. But you need root for that.
Then it's that, we cannot do anything I am sorry to say. At least my abilities stop here. You can maybe look for a way to root your phone.
And of course if you send me a private email with your order number I will certainly refund your purchase price.
Can you please tell us what version of the G3 are you using? Is it a carrier version? I know on some versions of this device it is possible to disable the voice command app. I keep this thread open for other G3 users to chime in.