How do I delete Discord so it can't redownloaded?

For reasons I won't go into I have banned Discord for my children and deleted the app from their phones. One of my children has figured out how to go into the purchase history and redownload it. How can I permanently delete apps from purchase history, not just hide them? And is there a way to block the app through screen time somehow? I do have screen time set up so that I have to approve all downloads but since it's in purchase history it does not ask. Please help mama out!