Connected to wi-fi, but "no internet"

HELP! I’ve had many connection issues since signing up with T-Mobile Home Internet. I have a new Chromebook that says it’s connected to my T-Mobile Wi-Fi, and that the signal is strong, yet when I try to open any web page on the internet, I get the “sad face” icon that says “no internet connection.” I’ve been trying to resolve this issue for hours now, and I’m unable to do it! Can anyone help? When I run the diagnostic tool, the following appears; WARNING; Local Network Can’t contact gateway, WARNING; Name Resolution Can’t resolve DNS from Android apps, PASSED; Wi-Fi,  FAILED; Internet Connectivity Can’t connect through firewall to HTTPS websites