Your home internet is offline

First. Check their site for official info on any possible local outages here;

https://www.xfinity.com/support/status 

https://www.xfinity.com/support/articles/check-service-outage 

Use a cell phone internet service, a public WiFi hotspot, or a neighbor's internet if you need to in order to check it.

Or you can use their Xfinity App: https://www.xfinity.com/apps  

Is/are the indicator light/lights on the modem lit steadily, or are they blinking ?

Yeah. It's offline. It may be a problem that is local to your premises. Did you report it in the app/schedule a tech visit ?

You may not have any choice unless you can try to fix it yourself/check the lines and connections.