Updated 6:47 P. M. U. S. Central Time July 12, 2019: added YouTube video search link as I was able to get YouTube search to work.
In a quick search, I found this article – How to battle spam on your landline phone: https://www.theverge.com/2019/2/12/18220804/how-to-stop-phone-spam-landline-scam-calls; it includes a link to https://www.theverge.com/2018/3/6/17071478/spam-calls-how-to-stop-block-robocalls-robots-scam-iphone-android for cell phones. For landlines, it depends on if it’s a VOIP landline or non-VOIP. For example, when I had Internet and a landline through the local cable provider, it was a VOIP line.
Check with your local landline phone company to see what they make available to address the problem.
I found a number of other articles from various sources that offered other strategies, tips, etc. to reduce or block spam calls for landlines. I used the following search parameters: landline phone options to avoid robocalls, although many of the search results included spam calls.
YouTube video search link: https://www.youtube.com/results?search_query=landline+robocall+blocking
