I found the same a number of times - I though service was out, but it was just no response from the ISP provided DNS servers (my router is setup to use the Southern Phone DNS servers). I swapped out to the Cloud Flare public DNS (1.1.1.1) and it worked again. I've found that if I set the router to use one of the ISP provided DNS servers and one public DNS server, I tend to get less issues - when the ISP DNS servers don't respond, it fails over to public DNS.
