The US has a national Do Not Call registry… you sign up online. It takes ~2 minutes to register and 30 days to take effect IIRC. Registering took my spam calls from several times a day down to several per year. The only ones I get now are political and people looking for the previous owner.

Edit: if you want to be proactive or vindictive you can report unwanted callers (or anyone using a robodialer) to the FTC.