Q: Unable to check for updates or install apps

Since last week (20.2.2016), I cannot install apps nor check for updates on my iPhone 6. I had iOS 9.2

I have tried everything

- reboot

- hard reset

- updated to 9.2.1 using iTunes (also updated iTunes to latest version)

- Logged out and in to my Apple account

- Reset network settings

- Reset to factory settings (including erasing my iPhone)

But nothing helped!!! I still cannot install/update apps from app store nor check for update (getting message: "unable to check for updates")

Any idea what to do? this is lasting too much time.

Thanks

Yuval