iPhone 6 not connecting to 4g

Im currently in Japan. I have an unlocked iPhone 6 from the UK, and put in my Japanese SIM card, which has been working (and still is working) in 2 other phones I’ve tried, including one iPhone 4 from the UK. However, in this iPhone 6, the service provider shows up in top left corner and it says 3G, but there is no internet connection whatsoever. Apart from wifi of course.

There are no profiles installed on the phone, and no APN option in settings. Can anyone help??