Arthur, you're probably quite right. But I have tried numerous methods to eliminate these marketing calls with limited success. Even those for my mother who passed on 2007.
However, my 'crazy' responses have secured an almost equivalent percentage of success. Amazing really.
Many of the calls I get these days are showing "International" , not much to do about those unless the callers register 'something' internally to prevent further ones.
Just my experience.
I do enjoy winding them up. Why not? they're paying with their time.
Great fun!