Tell HN: Cloudflare Hosted Illegal Content on My Domain

I got an urgent email from Namecheap this evening that illegal content was being hosted on one of my domains. I checked the DNS and I had set the nameservers to Cloudflare, but had never used Cloudflare for hosting.

I tried submitting an abuse form to Cloudflare, but their automated form claimed they did not manage the domain -- which is patently untrue, given that the IP resolves to their servers.

How could this even happen? And what recourse do I have, if any?