Thanks for reaching out to the Apple Support Communities! It sounds like you are having issues with your cellular data and roaming. Check out this article with steps to be able to Use cellular networks on your iPhone and iPad while you travel internationally . Specifically:
Get help with roaming
If you have these roaming issues while traveling internationally, learn what to do:
- If you see No Service in the status bar of your iPhone, go to Settings > Cellular > Cellular Data Options and make sure that Data Roaming is on. Then contact your carrier to make sure that international roaming is turned on for your account.
- If the date and time are wrong after you arrive, go to Settings > General > Date & Time and make sure that Set Automatically is turned on.
- Turn on Airplane Mode for about 30 seconds. Then turn it off again and let your iPhone automatically select the best network.
If you still need help, try another carrier network that supports your data plan or a different SIM card. To select a network, follow these steps:
- Go to Settings > Carrier and turn off Automatic. Wait until available networks appear. This can take up to two minutes.
- Tap the carrier that you want.
- Go back to the main Settings screen and wait for your iPhone or iPad to connect to the network.
Cheers!