We are having the same problem. It takes a bit of work, but once we track down the hosting provider we can usually get the sites removed that way. However, it’s absolutely wild to me that Shopify doesn’t have built in tools for preventing this! The fraudulent websites even say they’re are hosted by Shopify (which they aren’t), and I assume are copying proprietary theme files and code that Shopify should want to protect for its own business purposes. It’s not a good look, Shopify!