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There is some helpful info and tips in Travelling-abroad > Vodafone.
Roaming is unavailable on all Vodafone Basics SIMs as standard.
In your myvodafone ensure any relevant bars are off.
Either Live chat or customer service via phone can access your account and help you further with this situation via Vodafone Contact-us.
Perhaps Try your SIM in another phone and or try latching to another Network.
The network there maybe having it's own issues.
Just to advise Vodafone cannot guarantee everything will work while abroad.
Your phone may not support the frequencies and band's the network there uses.
That and check any settings in your own phone to see if it's blocking roaming.
That or if your phone is unlocked to all networks try a local SIM card or use Wi-Fi.
I wish you all the best with this situation.
Current Phone > Samsung Note 20 Ultra 5G - SM9860 Snapdragon.
Samsung One Ui 3.1 / Android 11.
If the issue is confined to data (you don't specify), as well as the bars on your account, make sure that roaming is enabled in the device's settings.
The other possibility is that international calling is restricted on your account it you've only recently taken out your contract.
It's disappointing to hear you're having problems using your international roaming @Petah.
As previously asked, is this just data that you're having problems with, or calls and texts also? Try the troubleshooting steps that @BandOfBrothers and @hrym have advised. If you're still having any issues, please don't hesitate to pop back to us and we'll be happy to investigate further.