Hi @brendafrancis ,
Are you getting an "invalid MML code" message?
If so you have already found out the answer.
It is a South Korean phone.
Researching online shows that for these phones to work outside of South Korea they have to be initially activated in South Korea, but even though this means that they are then unlocked and should work worldwide, it doesn't mean that they will be able to have all the same attributes as an identical phone made for a different part of the world or even the 'international" model.
To get certain facilities to work, others have rooted the South Korean phone and installed custom roms.
Here is a link, not really relevant to your particular problem, but it shows that others are having problems getting South Korean phones / tablets to fully function in other parts of the world.
You may have to find another way to recharge and check your balance.