Calls multiple times a day/week, no one ever responds to my "Hello?"

It may be a robo call or telemarketer. When i called the number back the automated message starts out saying "this call may be recorded for training purposes". I didn't wait to see if someone would come on the line.

Caller said they were from a law office and kept asking for my information. When I refused to give them information information they said they would send me a letter. I believe it was an debt collector attempting to collect an outdated debt.