Send them back to your ISP telling them to stop sending them to you.
Forward the whole message to abuse @your isp etc. without the spaces. With Unsolicited Spam in the subject line.
Or if better still forward them to the senders ISP and make sure you put Unsolicited Spam in the subject line.
Write something like "I am recieving too much unsolicited spam on a daily basis despite my attemts to filter it out and I will continue to return them to you until they stop".
It works for me.
Imagine if everyone did this everyday, do you think the ISP's would treat spam more seriously ?