Don't give up... it's a process converting a wild-caught fish to accept subsitutions in a captive setting, particularly one so specialized in feeding on live food items. There are very specific ques that are required for a predatory fish to strike at something. The trick to getting predatory fish to feed on non-living items is to change the ques required for a feeding response. That can take some time.
I have a spotfin lionfish that at present, refuses everything except live grass/ghost shrimp. However, we have started the process of converting it to more easily handled food items such as frozen krill and mysids. The process usually goes something like this: the fish in question will only take live - so feed it live stuff, just not too much - keep it a little hungry. Then, take the live food item and put it on the end of a feeding stick - I use a piece of rigid airline tubing with a dulled pin attached to the end via a very small section of flexible airline tubing. It sounds complicated, but most people have the bits laying around and its quick to make. Next, feed the fish from the feeding stick all the time. This way the fish will eventually associate you and the stick with food. Next, kill the live food item prior to offering it. Once the fish is taking the dead-live food item, try a piece of krill or mysid on the feding stick. You may have to alternate between the live food item and the frozen for a while, but eventually the fish should take the latter. After it does, there will be no looking back!
Like I said - its a process and some fish make the shift quicker than others. Wish us both luck!
Hope this helps.
Lee