Extortionists pretending to be debt collectors. Don't try to reason with them, they are simply illiterate scum. They don't care about laws. Stop answering and get a call blocker. Also make sure you report them to the following two agencies:
Read up on your rights here and also make a complaint at this government site: http://www.consumerfinance.gov/
Also file a complaint with your State Attorney General's office.
List of State AG’s offices: http://800notes.com/faq/attorney-general