I would call the manager back immediately and tell him that you believe the employee was engaged in fraud and theft. They have surveillance cameras all over the store, so you should tell the manager you want to come down and see the footage showing your transaction. This is a very serious situation as that employee literally stole from you.
This is pretty much the only possible saving grace at this point; video of the employee hiding the receipts and you not getting any merchandise. Otherwise, there is practically no proof of what happened since it was "picked up" and the employee could have forged the signature.
And yes, orders can be cancelled in-store. I did that last year during the by $xx.00 in TV series, gt a $XX gift card. I ordered online, but when I got to the store, I noticed that deal was going on, in-store only. So I had them cancel and then bought in-store to get the free gift card.
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