mobile data usage spike after connecting to overseas provider

[haltink]

I travel regularly to the Netherlands and other European countries.  I never exceed my 2gb mobile data allowance while abroad. Recently I travelled to Belgium and two days after arrival, I got a message that I had reached the limit of my allowance. I rang BT and they could see that this was not within my usual pattern and gave me one 1gb.  They also told me to turn of wifi assist which I did.  As  I did not want to incur further spikes in data usage, I then turned  my roaming off for most of the rest of my trip (except for the occasional checking of train timetables etc). I have been back nearly a week now and have been almost solely on WIFI and got another message that I have now only 500 mb left. I rang BT and was told that the main usage of my data was 'unclassified' and linked to Belgium. Is it possible that connecting to a foreign provider can cause an unexpected  spike in data usage?  I have never ever had this problem roaming in Europe. 

[Edinburgh-wg]

Mainly your phone updating in the background, such as maps, apps etc. You'd be surprised how much information is constantly shared with Apple/Google and other companies. 2GB is very little these days. 

Using apps like X and Facebook also leads to more data being used because they also use adverts which download as part of your allowance. 

You can turn on data saver which will limit your phone to only essential app activity. Also, restrict app updates to WiFi only. You can also use AdGuard as your DNS resolver to ensure that adverts don't load. 

[clever_trevor]

Might be backing up overnight as this would use data so set low data mode.

[Colin_London]

Think about activities that normally happen overnight on WiFi which are now happening over mobile data because you are not at home. Things like app updates and backups.

if you have an iPhone you can stop individual apps from using mobile data such that they only work over WiFi (eg. At home).