I've been subscribed to a UK based liberal democrat campaign and party news list for two years now. I have

- responded to several fundraisers and party organizers asking them not to email me anymore

- clicked the unsubscribe button/link when there is one(about 1/3rd of the time for some reason)

- reported as spam

- used various unsubscribe services/aggregators

all to no avail. At this point every time an email gets through I just report as spam and manually add them to my filter.