NEVER press any numbers. It let's them know they have reached a working number, and you will stay on their list. If you don't know who it is, don't pick up, just report the number on the donotcall.gov website.
This is not true. There is such an influx of scamming going on that it is difficult to keep up with the different numbers these scammers use. Go to the government website and see how they are working with this problem.