It sounds like what you've done is just purchased a billing add-on, rather than also enabling the roaming facility - this is what's needed for your phone to connect to foreign networks.
Did you do so, by texting ROAMING to 150 before leaving the UK? If not, you will need to enable roaming by contacting EE CS who have access to your account.
Either +44 7953 966250 from any working phone, or +44 800 0798586 from a web-calling app such as Skype.
