Our building has a trunk line. All outgoing calls give the same phone number on Caller ID. If they try and call it back, all they get is a ringing phone, no one at the other end. Maybe that is what they were calling.
Possibly, I'd call that a wrong number they should be calling the big 1800 national number, at least imo for customer support. My mom for example would not know any other number to call but the main one, these people act as if they no very little, no package, find # call.