Or you can try to turn off your router/modem and turn it back on 3 mins after. It will perhaps reset all the ip and hopefully it will give you a new ip for the phone.

If it's still not working, you may want to reset the router and reconfigure it..

Have you guys try to connect to another router ? You guys should try another router, like your friend's router. That way you can 100% sure if it's either the phone or router the real problem.