A lawyers office calling for my brother asking for a debt. harassment?

Hello, My brother moved out about 3 months ago. I get these phone called evey day asking for him and i tell them he dose not live here anymore, stop calling here. I did stop for about 2 weeks, then i got a call from this guy asking for him again, i told him again he dose not live here. This guy then told me that he is in serious trouble and i am a lawyer. He then told me he ows 5k to a credit card company now. Then this a-hole said told me my name address ect. and then treaten me. he said if i am not telling him info where he is ect. and if i am screening the call he would have me arrested. I was scared and gave him his cell phone #. he then told me i did the right thing and he would not have to file a case with the FBI. I have never delt with any of these fine folks. i have his # on caller id and its a 1-886