Phone is very data poor. All over country often 1 bar of 3G only. Sometimes nothing.

[JMA14]

Since getting a new iPhone with 02, the signal / data has been extremely poor. In various parts of the country often only 1 bar if 3G. Husband and daughter with other networks have no problem getting 4g. My phone is often not working when their phones are fine. I had no such issues when I was with Three last year. Something is not right with the data and / or the iPhone. Contacted O2 and the promised to monitor and call me back but of course they haven’t. 

[Cleoriff]

@JMA14 

Have you got the iData bolt on? (Needed for all iPhones to work correctly.)

You could pop instore and ask the staff to check it out, or contact Apple to run a diagnostic check

https://www.apple.com/uk/retail/geniusbar/