Debt Collections Calls Won't Stop

I have a person that continues to call me at home and at work. I have been turned into my supervisor because this person keeps calling, up to 10 times a day,and won't hang up. I can't understand the person calling, they don't speak english well and I have no idea who or what they are calling about. If I tell this person do not call my office ever again, that I can not receive personal calls at work, by law, do they have to stop making these calls to me at work? I live in Pennsylvania, in case the law varies from state to state.

Also, when I have spoken to this person I have ask several times to speak to someone that speaks english clearly that I could not understand what or where they were calling from, but they never have called me with someone that I can understand.