iPhone6 Blue screen of death after iOS 8.3 update

I have recently updated my iphone6 to iOS 8.3. And my phone keeps rebooting with blue screen.

I cannot connect to the wifi. If i somehow get connected to the wifi, the blue screen appears and my phone starts rebooting.

After the rebooting the phone switches on , but my wifi option is greyed out.

I have tried the following things already

1)hard reset

2)factory reset

3)upgrading the iPhone via itunes

4)restoring from the back up

I have even tried downgrading it to iOS 8.2, but even that doesn't work.

What can i do at the moment ?

I am stuck.