I would see if you can return the fish and get your money back or store credit. Since you've had the fish for a month they may not take them but they did sell them under the wrong name and this fish gets so much bigger than piranha so they should take them back. Then you have to decide what you want. Do you really want RBP's? If you do and that store doesn't have them, I'm sure someone here can tell you where you can get them. You could get some other fish that you like. Cichlids or how about some Tigerfish?