URGENT HELP

I just ordered a packet from someone and they told me when it arrived that they sent the wrong package and told me to wait for it to be sent back. Today I got the notification that I picked the package and to say if everything is OK for the payment to be done. What do I do????? I want my money back and I don't know what to do, I don't have the package and I can't pick it up anymore and I don't know what to do....