Your caller is a lying scumbag scammer calling from Jamaica (area code 876 is Jamaica). He is not with the FBI, he is a scammer and wants to frighten your mom into sending him money.

I have received calls from this man before - he has a thick accent and is barely understandable.  He has called before saying he is an ATTY and uses my mother's name and he wants her to call him back.   He has called saying something about Walmart and uses my mother's name.  When she tells him she's not interested and hangs up on him, he immediately calls back, leaves a message and uses her name demanding to know why she hung up on him.   These calls are all usually made during the day.    I just received a call at 10:15PM stating that he was from the FBI and that I need to answer some questions for him (he did not refer to me by my name or my mom's name).   I told him he must have the wrong number, and tried to hang up.  When I clicked back over, he was still on the line saying it wasn't and I needed to answer official FBI questions.  I told him I didn't understand him and he mumbled something and hung up.    I called my local police.