i can see where you are coming from too and it does seem irresponsible of the bank to lend him this money.
i suppose where im coming from is that to try and get him out of this seems the wrong thing to do for me, as he must learn that there are consequesnces to actions. if im being totally honest it sounds like you are making hm into a victim, who was preyed upon by the bank, but he clearly has some access to advocation and if he can hardly read, how did he respond to a letter that came through his door and have the wherewithal to make an appointment at the bank ? maybe he is better at orting thinks out than you think? i know this is not helpful, but it was the first thought that came into my mind, and i just felt i had to put it down.
in a way, he is not unlike any other teenage who discovers the "joys" of credit cards, and dosent have much concept of paying back the "free" money, but in a way perhaps this is a good thing to happen now, so he can, with help from you, make it into a lesson well worth learning for the future about budgeting and credit. He is in a good position having you to help him; i wish i had had someone to help me out in the same way you are helping this young man