Ah I see.

I saw in another comment that they are telling you to report the problem on Apple Maps, which makes me think they aren't understanding you when you say it's a problem with the GPS. I would make sure to tell them it's a problem with every app that uses GPS - Google Maps, Waze, Pokemon Go, etc. Obviously the button in Apple Maps isn't going to help you since it sounds like a problem with the GPS itself.

It sucks, but since you're outside the return window, it sounds like you will have to go the support route. If you talk to someone on the phone who seems to understand your issue, ask if there are any other ways to replace the phone, like a mail replacement program or anything.