You signed up years ago, then. They changed it since then. Now you at least have to wait a week. I had access for years, then I lost my log-in half a year ago or so, and I haven't managed to get back in since.
Since there's no official explanation anywhere searchable, and lots of outdated instructions like yours, it's a real hassle.
The site programming for e-hentai/exhentai has always been total shit. Try and search for the information on the forum. Mentioning "exhentai" by name seems to be a bannable offense, and searching on "sad panda" gets you a pile of broken links.
You can try creating an account, then wait a week, then clear your cache and cookies, then log in and try to access exhentai, and maybe it'll work, maybe not.