They only let the phone ring once or twice and then hang up. They never leave a message or wait for me to pick up. I have no idea who they are or what they want.
It's MRS Associates Debt Collectors. Here is some useful information about debt collections from the Federal Trade Commission:
Your rights (what a debt collector can and cannot do).
http://www.consumer.ftc.gov/articles/0149-debt-collection
How to tell a real from a fake debt collector:
https://www.consumer.ftc.gov/articles/0258-fake-debt-collectors
Here's some info on MRS Associates:
MRS Associates, Inc. was founded in 1991 and is based in Cherry Hill, New Jersey with additional offices in Arizona, Ohio, and Northern New Jersey.
Mr. Saul Freedman
Co-Chairman and Chief Executive Officer
Mr. Jeffrey Freedman
Co-Owner, Co-Chairman and Co-Chief Executive Officer
Mr. Darren Schulman
President and Chief Financial Officer
Mr. Eric Hunn
Chief Operating Officer
Mr. Michael Meyer
Chief Information Officer and Chief Security Officer