Like Fortnite and other Epic Games titles, Apple has disabled the option to download or re-install Battle Breakers on iOS devices. 

The game remains playable for players that already have the app installed on their iOS device 

More info

Other ways to play Battle Breakers:

Battle Breakers remains available to play on PC, Android: Epic Games App or Samsung Galaxy Store

How to get a refund:

Apple doesn’t allow Epic Games to directly refund players for iOS purchases and instead requires players to ask Apple for a refund. Please follow these instructions to ask Apple for any refunds for your Battle Breakers purchases: https://support.apple.com/en-us/HT204084