Honest question, why is it not the Cubs (Marquees) fault? Maybe the right term is Cubs issue. I had the same problem, until after 3 phone calls with Marquee CS, I cancelled the service.
I live in eastern Iowa and have Verizon ISP. As a WIFI based provider, it uses servers in large metros. Mine connection tends to use Omaha. So the Marquee App sees the server location and not where I physically am to determine whether I should be blacked out. It seems like Marquee App could override the ISP server location and allow access based on physical/credit card address.
Whether the "fault" is the Cubs(team) or MLB, baseball needs to get their blackout rules fixed. It's not like baseball can turn away fans. My best option might be to subscribe to MLB.TV at a little bit of a price premium. But the Cubs won't see that revenue. And my fear is MLB.TV will black me out because I actually live in-market for the Cubs. We'll see.