You can stop the tweet shipment anytime.
You need to signin first. (There are two signin ways, openid or email/password, see following section for password assistance). On successful authentication, you should be brought to a page starting with "Welcome back...".
Scroll down this page, until you read "Gimme a break". Right there, you have two choices: Delete your account or just suspend it.
Issues signin in
Please read instructions on this page.
Please read instructions on this blog post.
Feel free to contact us (well, me), I'll try to help you out with your issue. There is a page with contact information here.