Identify the Sender

The first thing you have to do is to identify the sender. This may not be the same company or organisation that actually spammed you, although in Roberts v Media Logistics (UK) Ltd it emerged that 'Kwikar' was actually a trading name (or division as the called it) of the same company sending out the emails.

Write a complaint.

Yes, I know, it sounds old-fashioned to write a letter. But you can use fax and recorded delivery, and you are pretty sure the other side got the message.