[Thanks to a tip from a loyal reader]
AT&T Call Protect offers more control over nuisance calls. This free service is provided through the AT&T network and features automatic fraud call blocking and suspected spam call warnings, as well as manual temporary call blocking through the optional AT&T Call Protect app. It's free but it will work only on relatively recent vintage smart phones. So, if you have an iPhone 5, Call Protect will not work on it, which should provide one great impetus to switch to a Samsung Galaxy S5 or higher on all of which Call Protect will work.
PS: If you call AT&T for any technical support, you will discover that AT&T has gone to a new voice-command answering tree that likely will win the award for WORST answering tree in the world. You might consider asking President Trump to look into the matter so that he can do his thing to make AT&T great again. In the meantime, if you need technical support, say "technical support" (without the quotes) at the first prompt, then say "voice mail" at the second prompt (without the quotes), and then, if there are any more prompts, just keep hitting 0.