You have to tell them to put your phone number on their internal Do Not Call list, which they are required to have.
That's also because, if they remove your number from their current list, and later get a new list, your number might be on that new list but they won't know your number must not be called.
They have been calling me for a few weeks, never after pm, but just today they accide nearly left a voice mail and i could hear faint conversation in the background so my guess is its political or telemarketer people.