Try completely ignoring unknown numbers and see how that works after some time. You can maybe stop your number from being passed along if they get nothing from it. If you don't wish to spend, not answering at all is free.
Call at all times of day and night. No caller ID except the number. Hope someone can track them. Have turned their number into the state Attorney General's office for prosecution.
Feature Films For Families calls continuously. They use a dozen different names and numbers to try and fool you. If you have ever purchased movies from Feature Films For Families, you will be on their list for ever. I have asked repeated to be removed from their call list, but they continue calling. I have told them I was on the Do Not Call Registry, but they laugh and say, "good luck with that!"