How do I stop voice mail after I hang up on a call?

[japark]

Galaxy s5, Sprint. I get several calls per week ( sometimes per day ) from Credit Card Services, or other solicitors. I immediately hit hang up to cancel the call. In a minute or so, I have a voice mail from the machine which I now have to delete.

Am I doing something wrong or is there a setting I don't know about. How can a machine call leave a voice mail when I have hung up on the call?