Who called from 4435644855

This number keeps calling people that I know or knew that are listed in my cellphone phone book.  Some numbers as far back as 5 yrs ago.  They leave a case number and threaten legal action. They say they are from Ft Lauderdale, FL but this is a Baltimore area code.

Does anyone know anything about this?

it's a collection company

I was told that the company name is ISA and that this is an investigator and that it would be for my benefit if I return the phone call

I get the same call.  I don't know if this an collection agency. Gave me some kind of case number and also threaten legal action.

They threatened civil suit and said it was imparative I call back.  I didn't like the sound of a threatening phone call.