Your post has been moved to a new thread, although the advice will be exactly the same as to anyone else with the same problem.
You have purchased a billing add-on, this reduces the cost of roaming but doesn't enable the roaming facility itself - which is what allows your phone to connect to foreign networks. This free of charge facility is not something you can enable in your phone, it's a network-level permission that is normally done by texting ROAMING to 150 before leaving the UK. Did you do this?
The phone setting you're referring to, is very likely "data roaming" - this simply enables mobile data whilst roaming. There isn't a phone setting for "voice call roaming" or "text message roaming", but that would be the equivalent.
