I've experienced many similar incidents – I've been running multiplayer game servers on these "discount" server providers for a while now. They receive umpteen requests per day about spamming, hosting pirating/other illegal content, botnets, etc with only an associated IP address.

Vultr has a nasty habit of forwarding these directly to the current holder of the IP address with a dire warning that your account will be shut down within 24h if no action is taken, regardless of the timestamp of the complaint. Abusers just create & destroy servers frequently frequently to acquire fresh IP addresses to host malicious content on. It became a morning routine of copy+pasta responses to these emails to keep the servers online.