One of my pacman refuses to take anything from a tong unless he sees it move freely on it's own first, he's weird. Have you tried just letting some crickets run freely in it's tank? Maybe he's scared of the tongs and prefers to hunt on his own. You've probably tried this but I'm just suggesting it anyway, I hope he eats for you. Also, rip the hind legs off the crickets so they can't jump making it much easier for your frog to catch them. Good luck with the little guy!