I never answer numbers I don't know, they call but leave no message

Call back gets, "Thank you for calling national credit adjusters.  They are debt collectors and have a bad reputation.  Whatever you do be sure you know your rights when dealing with debt collectors.  NEVER acknowledge debt on the phone.  Insist that they prove that you owe this debt in WRITING including papers from the original loan and original lender.  Here's what the FTC says about debt collection:
https://www.consumer.ftc.gov/articles/0149-debt-collection

Also read about phantom debt
https://www.consumer.ftc.gov/blog/lesson-phantom-debt-collection

Here are the basics from the FTC:
Quote:If you think that a caller may be a fake debt collector:

   1 Ask the caller for his name, company, street address, and telephone number.
   2 If a caller refuses to give you all of this information, do not pay!
   3 Stop speaking with the caller.
   4 Do not give personal financial or other sensitive information.
   5 Contact your creditor. Read Debt Collection for a list of your rights.
   6 Report the call to the FTC and your state Attorney General's office.
Finally, here are some reviews (complaints) about this "company."
http://www.ripoffreport.com/r/National-Credit-Adjusters/Hutchinson-Kansas-67504/National-Credit-Adjusters-National-Credit-adjusters-trying-to-collect-a-debt-that-has-alre-244317