I get calls at home. I use to tell them that the person they are looking for is no longer at the number. But the idiots kept calling me. So now I take a message for the guy. Then after I have the callers name and number I call back and ask to speak to the person in charge. I then tell them if they call this number again from their company I’ll report them. Its worked wonders.
Most of the time they wont give you any information on who they are unless they think they might get in touch with whoever they are looking for. So taking a message is the best way to findout what company it is.