You can't stop the emails arriving on your email provider's server. If you use web-based email you therefore can't prevent that mail going into your Inbox (or your junk folder) since you're simply viewing the files on that server. However if you use an email client (such as Outlook, Outlook Express, Windows Live Mail or Thunderbird) you can prevent the mail being forwarded to that client by using Mailwasher:
http://www.mailwasher.net/
You seem to be learning the hard way that your 'main' email address should only ever be given out to trusted friends and colleagues. When ordering things online, or signing up to web forums like this one, you should always use a different email address.
Chris