Originally Posted by After Shock Media

You do not need a lawyer for small claims cases which are typically either 2500.00 max or 5000.00 max.
Next as a minor you can not enter into a contract and you are not bound by their TOS, so they can not change it on you. They must pay you since they failed to get your age before becoming their independant advertising contractor.
Only issue that sucks for you is you say your in Japan so odds are airfair will cost you just as much as you stand to win.