Robo Calling is on the rise and while the carriers of the world are working on new protocols to help cut down on them here are some simple suggestions to help protect against unwanted robocalls...
Insert an auto attendant in front of your direct dial, ring group, or call queues.
Have your end users notate which numbers are robo calls from their call history and then you can actually add them to a block list in the phone system.
Go to Settings - > Blacklisted Numbers
You can then either import from a CSV or press ADD and enter the caller ID and press OK