I can see this community in my feed but at the same time this community can't be found. Is there something wrong with my instance?

So I have set up my own Mastodon instance and it's empty. What should I do to fill up my instance with content? And how do I do that other users of Mastodon on other instances see my "tweets" on my instance?

cross-posted from: https://random-hero.com/post/51002

Hello everyone! Recently I have removed a couple of bot users from my Lemmy instance via DB query (I removed them from person table). Those bots were subscribing to hundreds of communities on other instances which I don't really want to spend resources on fetching new posts and updates.

I have purged those communities from my instance but they keep reappearing. As far as I can tell, this happens because other instances still "think" that users from my instance (bots, which don't exist already) are still subscribed, and therefore send updates to my instance.

How can I completely get rid of those communities?

There have appeared hundreds of communities on my instance I have never searched. Where do they come from? Is it some spam attack? How do I prevent this, and how do I get rid of them?