rdmix

So I've gotten my ksb for about 4 days now and its 3 months old. I tried feeding it today and the pet store told me that it has upgraded to a large pinkie, so i tried feeding it to him in a tupperware container with air holes and i tried both covered and not covered. It's still not eating, it hasn't eaten for about 2 weeks now and I'm getting a little worried. He pokes the pinkie around but doesn't bite it or anything, he'd push it around the container and try and escape the container. Basically I'm guessing hes playing with his food... Should i be worried about this? and oh, last time he got his weight checked he was 20g and about 11 inches. Thanks