You mark the content posts to +18 in your account?
That's not enough; you need to change the account's content to NSFW/+18. This limits access for minors (and bots consider your content adult, so it gets through). You can change your content to "Mark media you post as containing material that may be sensitive." I know that X automatically changes your account if you have a consistent posting pattern of this type (you can also mark each post as NSFW content, which protects your account from being taken down by a bot for this reason).
I'm sorry this happened to your account =/ try to recover it or upload a new one.