If you receive unsolicited commercial email, you are entitled to inform the sender of their error and of action which you will take should they repeat the offence.
Here's a blog posting from one who's taken legal action against spammers and won. It's not difficult – you just have to be aware of the relevant legislation and be sure that you've not
given them permission to send such commercial mail.
See also http://www.revk.uk/2014/12/notice-before-action.html
, which references sections 22 and 30 of the Privacy and Electronic Communications (EC Directive) Regulations 2003.