It's a debt collection agency, and reportedly a hostile one.
Whether you are called a debtor or some collector thinks you can flush one out, you have rights and options. Most are simple to exercise if you only learn how. The FTC and the CFPB can start you on your homework. See also if your state laws grant additional or stronger rights.
official FTC guidance and staff opinions on the FDCPA, PDF copy of the Act
CFPB reiteration of the Fair Debt Collection Practices Act