Where are you?
What membership do you have?
Are calls and texts working?
If you are roaming in the EU on a Guido membership then data should work.
But not if you are on any other membership or are roaming elsewhere.
If calls and texts are working but data is not then check your internet/APN settings.
If the APN field has changed from 48months.liffeytelecom.com to something else then change it back to 48months.liffeytelecom.com, switch airplane mode on and off and then try again and see if data is now working.
Hope this helps.