Regardless of any billing add-on, your ability to get coverage abroad (which calls, texts & mobile data rely on) is dependent on roaming being activated - which allows your phone to connect to foreign networks. Furthermore, "data roaming" is simply a phone setting that enables the use of mobile data whilst already roaming. If you don't have a mobile network connection, then data usage is impossible with or without the "data roaming" setting being active - thus that setting is futile
On pay-monthly, this needs to be enabled manually - usually by texting ROAMING to 150 before leaving the UK. Did you do this?
If you now find yourself abroad without having enabled roaming, your only recourse will be to contact CS to request it activated. You can either contact +44 7953 966150 from another working phone, or +44 800 0798586 using a web-calling app such as Skype over WiFi.
