Company spamming me. Creative ideas to get them to stop?

I've unsubscribed about 10 times from emails from Web Summit and even got human responses several times assuring me I will get no further emails from Collision Conference, Web Summit or any other events this company runs.

However, they continue to bombard me with emails.

It seems to be coming from an automated address that's probably not checked by any people (p@news.websummit.net) so what can I do to get the message across that I don't want to hear/have anything to do with these guys anymore?