iPhone 14 pro mobile data not working

Currently in Vietnam but live in the UK. I’ve been travelling for 8 weeks now and using local SIM cards for data. A few days ago my 4g stopped letting me connect to the internet even though the logo was in the top right corner with full service bars. Thinking the card had just run out I replaced it. This worked for about 4 hours before stopping again and I had the same issue. I tried buying a data package from my UK provider and using that temporarily, again the same issue. After being able to get to somewhere with WiFi I was able to connect and search my issue. This is when I found out I should reset my network settings. I did this and everything worked as normal for 24 hours before the problem repeated. After spending over an hour on the phone to apple support yesterday (probably incurring hefty call fees) the problem appeared to be that I wasn’t on iOS 17, despite having only done a software update to the “newest version” that day. After the update my data was working fine until about an hour ago when it suddenly stopped again. I’ve gone through all the steps explained to me by apple support yesterday and still it isn’t working. Any help or advice would be much appreciated as I really don’t want to call apple support again with international call rates.