When I talked to Shopify, they said they would take it down if it was another Shopify site, but since it wasn’t, there wasn’t really anything they could do. I went through a lot of the steps listed above, and had success with the same solution - I was able to look up the domain in GoDaddy and find out it was through PublicDomainRegistry.com. I contacted their support and reported the site and they had it taken down withn 24 hours.