I just ignore any call that's not programmed in my contact list. If it's important, they can leave a voicemail. About 5% of telemarketers try to leave a voicemail, but robocallers are bad at it. I can easily delete those after listening to the first few seconds.
I know the NoMoRoBO app works. It absolutely plagued the auto-dailing, robocall operation a company I worked for was trying to do.
Someone calls you, and if they're not on a whitelisted list of numbers, they get: "This call is protected by NoMoRoBo. To connect to your party, please dial the number [random 2 digit number]. If you are a telemarketer, please regard this as your notification to place this number on your do not call list and do not call again."
Official instruction was to disposition the call as a bad number (They know they'll never get through). This is what you want.
Sadly, it's 2 dollars a month. To most it's not worth it just to stop some calls, but some people REALLY do get plauged, especially if they've been scammed before, they end up on a "suckers list" and every single scam company starts calling them.