Sometime Wifi connection and Phone connection was lost

@Tkato

Much of what you've described sounds like it could be wifi related.  Are you able to duplicate the issue with a computer connected directly to the modem?  Make sure when testing that you push the reset button on the modem after plugging in a new device otherwise that device won't receive an Internet connection.

I didn't try but I think modem should be work, because Wifi signal is available when no-connection. Recently I always pushed the reset button when encountered wifi no-connection. When Wifi connection was lost, we can't use phone too. It is not convenience for us. Could you please tell me why happened so many times?

@Tkato

If the problem is indeed only affecting wifi connections via the router that would be an issue the router's technical support would be in a better position to address.  We can check the quality of the Internet connection for you if you're able to try connecting directly to the router.  

I think there is a bit of confusion here.

First, and I don't mean to offend, and I apologize if I am incorrect, but it seems as though Tkato's native language is not English.  It is either that, or the problem is not being described very well.

Second, there could be an issue where the cable went out completely, for all services (TV, Internet, and phone).  I had a complete outage a week or so ago.  Before I realized it was a complete outage, I had first just noticed my Android phone would not stay connected to my router.  It would power up the WiFi radio, but after 2-5 seconds the WiFi radio would shut down.  I rebooted the router, but still had the same problem.  I then noticed the lights on the modem were blinking like it was trying to sync.  I powered off the modem and back on, but it still did not acquire service / sync.  I then went and turned on a TV and found that TV service was down too.

Moral of the story:  Complete cable outages can cause WiFi outages.