K, you have been a victim of identity theft, or, they are fishing to get your info to steal it and set up phony accounts in your name, leaving you with the bills. This is what you need to do, if it was a physical letter, make a copy, or several, and send on to the credit bureaus in your name, give your info, its secure. They will flag your info, and if someone else comes up, they can prosecute. Also, file a police report, along with going to the social security office to see who else might have your info. Its a royal pain, but this is what you need to do to protect yourself.
Second, if it was online, make a copy and in your files, forward it onto your anti virus co, and I think you can also find an actual anti phishing website to send it to, and they also will follow up on it.

My ex was a stock broker, and he said you are not responsible for this. Do what I said, send a copy of the police report to the brokerage firm, bank who claim you did this. They will then, remove your name and you should be free and clear. Also, since you are a minor, you are not legally liable for this either. Good luck.