Connected but no internet??

It's been over a month now that my internet has been giving me problems. I am not able to connect some devices as I am able to with others. And even though devices say connected, internet is not available. I have unplugged my modem, reset my modem, reset my devices, everything I have been told to do every time I have called xfinity for help. Still nothing. What could be wrong?? We did have an outage which since then my internet stopped working the way it used to. The ethernet cord especially does not connect to my devices. I have exchanged the modem for a new one but it is still giving me the same problem.