HARD RESET YOUR IPAD.
On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons. On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button.
did you try resetting network settings on your ipad too when you did on the wifi router? If not do it:
Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.
this will not erase any of your data- just reset network settings, but its always better to have a backup before you do it. Good luck