If it's legal in your state, tape the calls and each time tell them to put you on their do not call list. I believe they can be fined for every call after you inform them to put you on their do not call list.
In any case be sure you're on the national "Do not call list" at:
https://www.donotcall.gov/default.aspx
The problem is that they are recordings. I don't have caller ID either.