disabling data roaming on Nokia 6.1 (Android 10), service provider o2 (UK) I'm in Japan with my Nokia 6.1, running Android 10.  My service provider is o2 (in the UK).

I've done everything I can find to disable data while here:


Settings / Network &amp; Internet / Mobile network / Mobile data: OFF
Settings / Network &amp; Internet / Mobile network / Roaming: OFF
sent o2 a "NOTRAVEL" SMS on their 23336 number


I can no longer find my "Data roaming" option, but believe I have also turned it off.

Nevertheless, when my wi-fi fails, my phone has been switching to data over 4G, incurring hundreds of pounds of charges.  I have therefore selected "2G" for "Preferred network type". o2 are not helpful.

Is there a simpler way of killing data over the phone networks?  If it's "Data roaming", where should that option be?
Selecting 2G as preferred network is the wrong decision as AFAIK Japan has no 2G network anymore (has been switched off some years ago). The minimum is 3G.

Because of VoLTE the definition of "data roaming" is become a bit complicated. If your device connects to LTE and has VoLTE enabled it starts a data connection. A lot of providers fail to identify those connections as "Voice" and charge them as data roaming. Therefore VoLTE connection start-up are charged as data roaming. 

Hence it is very important not only to disable data roaming but also disable VoLTE feature!

I also run into this problem on two-day trip abroad where my provider wanted me to charge data roaming for a few bytes every time when I switched on my phone or disabled Air-plane mode. Back from my trip I found a few mobile data roaming charges on my bill even with mobile data roaming disabled (phone has VoLTE capability). After complaining at my MNO they removed them from my bill by goodwill.