Domain claimed by malicious account

We had a domain that was pointing at our Cloudflare nameservers, but hadn’t yet been added to our account. It seems that in the meantime someone else has claimed this domain with their account and pointed it to a webhost and distributed malware with it. The domain was subsequently suspended by the national authority for this.
We’re trying to get the domain reinstated and added to our Cloudflare account, however my Cloudflare support ticket asking about it (#2276162) was automatically closed for asking about a domain that isn’t in our account already.
What are the steps I can take?

That’s never a good idea…and now you know why. Someone else with the same name server pair beat you to it.

What happens when you try this? It’s quite likely it’ll get added to your account, but with a different name server pair, which is perfectly ok.