This is exactly why we have the Digital Millennium Copyright Act (DMCA). In order to not be liable for theft, Apple is legally compelled to remove stolen intellectual property, such as your game, as soon as they are notified of its theft.
If your thieves want to republish their game, they must submit a counter-notification, a legally binding document stating that they didn’t steal your property, but if they did, they may not submit that notification.
If they do, your only option is to sue them, which is expensive and tiresome but may be worth it, if you truly have a claim.
There are processes in place for you to seek legal recourse, even as a small publisher. Use them.