ACS incorporation Cash Advanced payments Internet

A man that goes by the name Robert Brown had emailed me saying I owed money and that if I didn't pay then they'd use my SSN to find where I work and send a sheriff to my home to summons me. I asked for a phone number but according to them as a collection agency they do not have a phone number since they work in the back offices.

 I've been in collections before and know for a fact that they all have phone numbers to get ahold of the person they would like to get ahold of. I'm not sure what to do and would like for this to be looked into. I've never borrowed money with my SSN unless somebody else has.