iPad Activation Error - Please restore & update ios, "Cannot complete Activation Error"

After a random Reset; I found my iPad 3 on the "hello screen" just as it were New.

iPad 3 Wi-Fi, a1461 - s/n DMQJ88U7DFD1 with iOS 9.3.5 installed currently.

When I started to swipe through; it went to the Hello Screen, Language and Network Screen; then this Activation Error page appeared.

I have hard reset the iPad,

updated the driver through iTunes,

restore process, letting it choose the driver,

updated the driver through PC device manager,

manually installed iOS 9.0

We have 2-iPad 3's that broke within a week of each other; apple support wasn't much help.

They said they are older iPads Apple no longer supports them and may have disconnected them from the server?

Help I am stuck!

We operate a (low income) preschool program and badly need these iPads to work again.