Real time chat in general and discord in particular. Discord cannot be self-hosted, so any support message history will be completely reliant on the goodwill of discord. Another problem with using a chat channel for support (slack has the same problem) is searching for things you know are there but are impossible to find again.
And an ISP to host it on. As we know, if you don't self-host your ISP then you're beholden to the goodwill of a large corporation who could shut you down at any time.
I see these as complimentary, knowledge base for search and self support. Email for well documented transactions or low priority questions. Slack/Discord to avoid making phone calls when looking for real people responses quickly. Phone for emergencies.