OT: How to stop UltraDNS sales people calling

Hi, I am really fed up of calls from UltraDNS - we seem to get them every few days. We don't need their product. We've tried saying no, and additionally we've tried putting people on hold indefinitely, trying to be enough of a nuisance to drop off their sales call list (works with UK telcos - try it). I just had a guy on hold for 18 minutes before taking him off hold to say that we didn't want their product, and could he please stop calling. He told me he would still calling until he got through to the right person. I am the right person. In the interest of Anglo-American relationships - any Neustar people on list willing to help ?