Start with your Paypal account.
Check off all the Paid items you have received.
Open the Details on any you have not received.
Is it there?
If not contact the sellers of the items you have purchased but not received. Ask if they have a customer with a similar problem . (The seller may have mixed two shipments.)
If none of that pans out, as I understand it, if you recieve unordered merchandise in the mail, it is a gift and no payment is required.