I believe you are right about the Post Gazette. I also just cancelled my subscription a couple of days ago and they have already called here 3 or 4 times.
From other threads I called Telstart Corp at 1-866-733-0851, dialed 0 for the operator, gave them my number and they said "it might be a glitch" (whatever) and they said they would remove me from the list.
Calls received from this number every day multiple times, when answered no one responds. Call the number back and noone answers. I am not even near the Pittsburgh area for a newspaper if that is what it is to be calling my home.
They call for different paper companies. I live on the opposite end of the state and they call about a local paper out here. Try calling the 1-866-733-0851 number. I just did and they said they would remove my number. I guess time will tell.
based on a google search of the name, someone else referenced a company called 'Telstart Corp' and said it is affiliated with the Post Gazette. That might be what he said in the phone call. I also recently cancelled a subscription to the paper so thats probably why they're calling me.