The greatest middle finger you can give these spammers is not to answer their call. This number called my home phone today. The phone rang about five times. It stopped for a second and started again. Ignore them. I have noticed these calls tend to increased at certain times of the month. Either at the end of the month or near the beginning. I get very few of these calls during the middle of the month.
I get so many of these calls it's impossible to block all of them. What I do is keep a list with the date. If they call a 2nd time I block.