iPad mini. All connection lost!

Hi- all of a sudden I'm unable to establish any internet connection at all in spite of a) having cellular (and plenty of data available on the sim) b) having working wifi in the home and c) pairing with my iPhone.

The curious thing is that the icons in the top left are showing normally for my cellular, for the wifi and for pairing but absolutely no connection for internet email etc etc.

My iMac and iPhone are both connecting normally to wifi and cellular.

I've reset network settings, tried turning off Wi-Fi networking, tried rebooting my iPad several times all to no avail.

I've even tried a full reset (erase all content and settings) but this won't progress as needs to verify Apple ID password - impossible when not connected.

I've tried restoring by connecting to my iMac - error message 'device no longer connected'.

What is going on???? Any help appreciated!