If WiFi shows connected but the internet is not working, the problem may be your router, phone, computer, DNS settings or internet provider.
First, restart the router. Turn it off for 30 seconds and turn it on again. This fixes many connection problems.
Second, forget the WiFi network and reconnect. On your phone, go to WiFi settings, select the network, tap Forget, then enter the password again.
Third, test another device. If all devices have no internet, the problem may be the router or internet provider. If only one device has a problem, the issue is likely on that device.
Fourth, check whether your internet bundle or subscription has expired.
Fifth, on Windows you can use the Network Troubleshooter or run these commands in CMD as administrator:
ipconfig /flushdns
ipconfig /release
ipconfig /renew
If the problem continues, contact your internet provider.