there are device that you can get. but have no personal experience with that
How To Block Unwanted Calls
Got a phone? Then chances are you get calls from scammers. Scammers don’t care if you’re on the National Do Not Call Registry. That’s why your best defense against unwanted calls is call blocking and call labeling. Here’s how to block and report unwanted calls on cell phones and home phones.consumer.ftc.gov