if they email you again send a email saying you will sue if they dont stop.
my friend kept getting emails from this thing that sent you a joke everyday. nothing could stop it. in the end she sent a random spur of the moment, desperate last attempt to get them to stop, email,i think it went somthing along the lines of "WTF stop sending me these f*cking emails or I'll sue you!!!!"
about 5 mins later she got a very formal reply saying they had canceled sending her emails and were very sorry for the inconvinience....XD