App for dialing by voice doesn't recognize a contact

I try to use an app, i forgot it's name now, that enables to say the contact's name (one of the contacts in the phone address book) and the mobile will dial the number.
I had a contact who's name was in hebrew. i changed to an english name so the app. will read it, then tried to say the new name. the app. said it's not in the contact list.
What i try to do is use the mobile in the car, where i can't touch it.
I enabled voice commands in android, it's written there that i have to say "answer" and "reject", but i can't use it. how?