Xfinity app switches to previous window if I try to scan QR. + I lose my smartphone connection the second that I remove the coax cable

Brand new phone, and I have been trying in vain to activate my new modem Comcast told me I should have ( though the old works fine). i tried using the Xfinity app but it will not scan the QR code on the "Let's activate" brochure that comes with it. The app repeatedly  switches back to the previous window the second I try to scan the QR .

Also, I lose my smartphone connection the second that I remove the coax cable to connect it to the new modem (I have both wi-fi and wi-fi calling, Bluetooth, NFC activated).

Plus, on a previous attempt to manually set up the modem, I someone changed the modem login creds to one I do not know.