@Helen18
What issues are you suffering? and where in the world are you.
A Few checks to do
1. Choose a different network
2. Check Mobile Data is set to allowed for Roaming
3. Check your time is correct
If you message O2 on Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG) , they should be able to help you with this
This is not customer services and we dont have access to your account
I do not work for o2 or any VMo2 /Telefonica/Liberty Global Company
