Banned for breaking rule 3.
Edit: For more context with regards to your bans, consider the following: this is a longform discussion platform (a forum), not a chatroom.
does the reply "oh" meaningfully contribute in any way to the conversation at hand? It certainly didn't in the case you got banned.
is that extremely subjective and up to the moderator's discretion whether or not you get banned? yes, but I try to be fairly consistent. I have no reason to be sneaky about my bans, and there is no hidden agenda with why I banned you.
I'm not expecting everybody to write an essay with their posts, but put a little bit of effort into it - posting for the sake of posting, without any actual content, is godawful. Furthermore, I recommend you read the Guidelines since evidently you missed rule 3.