You can't really get the money back through the bank, once it's finished and credited into the other person's account. Depending on the value, you could possibly involve the police, or if you have the other person's details, then file a Small Claims Court case online.
But basically, don't expect the bank to be able to give you back the money straight away. Their only responsibility in this case was getting the money to the destination you asked for - they won't be really interested about what the payment was for, or whether you received the goods or not!