I saved an email from a long time ago about what to do with with these automated calls.  Don't know if it really works but I guess it is worth a try.

What you can do after answering, if you notice there is no one there, is to immediately start hitting your # button on the phone, 6 or 7 times, as quickly as possible This confuses the machine that dialed the call and it kicks your number out of their system. Gosh, what a shame not to have your name in their system any longer !!!