If you have purchased some recent items from eBay, checkout those sellers, sounds like they have posted to the wrong buyer.
Click on the seller's listings, then down the left sidebar click on Sold. If you find the item there, send that seller a message that you have received their item in error, for them to send you enough money to cover a fully tracked return postage to return the item back to them.
Do not be fobbed off with sending to the correct buyer, it goes back to the seller.
If this is not the case, and no one else in your household knows of this purchase, google Brushing Scam see if that applies here. I don't think it does as crocs are not a cheap item and this scam involves cheap throwaway items.
My feeling is a seller you have dealt with and they've sent to you and not the correct buyer.
@sparklestar1979
