Since 2003, the Do Not Call Registry has been accepting registrations and registering complaints regarding many types of unwanted calls.
Some of the worst offenders of the Do Not Call request are callers who've been told that they're calling the wrong number and keep calling it anyway. Also, callers who've been calling references who had never given that company permission to contact them on a loan or lease to try and find the original debt owner.
Here is an overview of the number of registrations and complaints throughout the country:
This chart shows that the number of new registrations has been on a steady decline over the past six years, and this could be contributing to continuance of robocalls.