[Q] roaming data turned off but there's still usage record. N9005 HK 4.3 MK1 topic

I have never enabled the roaming data option in the phone but in my trip to the states, there was tiny data usage everyday and I was charged for around US!!! I guess it is AGPS's data download but there's no way confirm.
it's the first time I have this issue with android phones. anyone seen similar issue?