i get lots of missed calls from this number..who are they?

Caller ID says ist's POTS.  
Don't have any idea who they are.  I answer the phone and say nothing.  An exasperated person on the other end keeps saying "hello?  Hellllooooo?" And then they hang up.  There are lots of other callers in the background having conversations.  

A Google of the phone number says it's from Ontario Canada.  Are they exempt from our Do Not Call lists?

Caller ID says ist's POTS.  Don't have any idea who they are.  I answer the phone and say nothing.  An exasperated person on the other end keeps saying "hello?  Hellllooooo?" And then they hang up.  There are lots of other callers in the background having conversations.  A Google of the phone number says it's from Ontario Canada.  Are they exempt from our Do Not Call lists?