The best way I have found to handle them is to ask them to wait just a minute, lay the phone down and go back about 10 min. later and hang up the phone.
I've done that before. I was told that they cannot hang up and make another call for a few mins so it ties up their lines. Not sure if true, but I have done it several times.
At our old number we got the same # that called every night around 6pm. We never answered, but they continued to call. This went on for months. I would figure they would quit after several missed calls, but not these people, don't even know who they were.
Worst one was at 8 am on a Sunday morning for 3-4 weeks in a row, local newspaper trying to sell us a subscription. finally answered one morning, told them I get what I need from their website...free so don't need to pay for their paper.