I have a small problem. I have 4G device (samsung Note3), 4G sim and 4G goodybag. In UK the data running in 4G. In Europe running in 3G only, even in 4G area. Why?
You will also need to make sure (in addition to having credit) that your phone is capable of receiving the roaming frequencies used abroad, it varies with country.
Check your phones 3G/4G frequencies on GSM Arena
Then cross check those frequencies on Mobile World Live
Also dial *100# to find your balance as you will need it to roam, roaming settings should also be enabled.