This definitely feels like an attack. One time I forgot to update my name servers after removing the domain from DigitalOcean and some spammer took it over. Another time I wanted to use DigitalOcean with my domain but I can't add it, because someone else has registered it.
After removing the domain from DigitalOcean did you use the domain anywhere else? It just seems strange to me that you can forget about a domain after explicitly removing that domain from a third party provider.
