You said you restarted your phone. Did you try a complete hard reboot by holding down your phone's power button and selecting “Restart" from the popup menu?
If that doesn't work, try resetting your phone's network settings. Go to the Settings app and type “Reset Wi-Fi, mobile, and Bluetooth” in the Search bar. Select the option and follow the prompts.
You will be asked to re-select your Wi-Fi network to connect to it .