internet service not available

Within the past week I'm having issues with my internet service not available.  I have checked all my connectiions, rebooted my modem, done a speed test, and everything checks out good on my end.  I tried connecting with my cell phone same results "Web site not found".  I can turn off wifi and connect to the web by data connection.  The service seems to come and go all during the day, "example currently internet is working about 1 hour ago could not connect to internet by wifi".  I check to see if there was any outages in  my area stated everything is good on your part, so what is going on.

Regards,

David