It really depends about what you did. If all you did was scam an account from someone who was selling it, you won't get in legal trouble, as long as there is no proof that you sold the account. You cannot gain money from selling Blizzard products, but scamming is perfectly fine.
Threats from his dad won't do much, unless he is willing to come beat you up in person. But remember it depends on what you did. If you did something illegal like sending fake photo IDs used in many scams, then you will be in shit. If you faked a notary, then you should go suicide right now. If you keylogged someone's information, then you will get into trouble. Get my point?
Scamming WoW accounts that are being sold is...legal.