Free spam call blocker

These online Trading Brokers have somehow got my phone number. They have called me for at least 4 years weekly, The calls must be in the hundreds if not thousands. I have repeatedly asked them to remove my number from their call lists, But they keep calling. Sometimes they are rude and threating and will call back numerous times if I hang up. They work in a boiler room environment and are just look to exploit people into their dodge trading platforms