Q: icloud data connection broken on iphone

Hi

Since I updated my iphone 6s to IOS9.3.5, I have been unable to get my icloud to connect over the O2 data network. It works fine if I have wifi on, but if wifi is off and I am relying on 4G, and I try to log on to my iCloud account I get the verification error saying I am "not connected to the internet".

Yet safari works fine and I can browse the internet - so I am connected...

The same issue has occurred with my imap email accounts which are hosted by 1and1. I cannot connect to collect email unless I am connected via wifi.

I have called O2 - they say it is not them

I have called 1and1 - they say it is not them - proven by the fact that my email settings work via wifi.

Any ideas please?