It is against the law. But they're crooks so why should they care about the law? You might want to invest in a call blocker or at the very least, don't answer calls from numbers you don't know.
They call me all the time.. The national do not call registry is a typical government program. The politicians make a big media event about it during election time, then no enforcement or fines! No one in the government will enforce it. Makes me sick. This is why we are fed up with Washington DC!
The fact that many of these telemaggoter operations are based overseas makes it impossible to take action unless the country of origin is willing to get involved.
The Do Not Call registry is for sales calls only, so if they are not asking you to buy something then it's legal. If you are being asked to buy something, then it's illegal.