Hognose usually won't eat off tongs until they get bigger. Cosmo has been with me since this past March and has gone from 11 to almost 60 grams and still won't eat off tongs. I just let him know it's there with tongs, set it down and walk away. It's always gone within a few minutes.
Don't be discouraged, sometimes they just need to settle in before they're ready to eat.