Hello!  I've actually had your issue happen to me once where an Item was fully canceled and shipped anyway.  Sometimes one computer system doesn't know what the other computer system is doing, or the item shipped before it was actually canceled.   Regardless DO NOT REFUSE THE ITEM.  If you do, it could take weeks or months for you to receive refund as it is not considered a valid return.  You can either call Customer Care to initiate a return, or follow the instructions here to get an RMA and ship the item back.  Last time I checked you do not have to pay for shipping the item back to Dell, especially since it was canceled.  
This is the worst. I placed an order for my parents on Thursday night, joined a chat to cancel it on Friday morning (1), was referred to a phone number so called to cancel, waited for around 10 minutes to speak to an agent with no luck, called back an hour late and spoke with someone to cancel the order (2), was assured that the cancellation was processed. Checked my dad's email yesterday only to find that they got a shipping notice over the weekend. Logged into the chat again (3) and got transferred (4) then because neither one could help me, I was directed to call. Called (5) and then got transferred again (6). None of the agents listened to my initial concerns/questions, even though I specified multiple times that I had ALREADY cancelled, they kept trying to route me. Annndddd I just got an answer back from the question that I sent on Friday, asking to confirm the cancellation, letting me know what I already know...that it's too late since it's already been shipped (7)... This never should have been shipped. I want to make sure that we will not be responsible for shipping this order back. This is a major inconvenience and I've been run in circles. This was supposed to be a surprise from my parents, but now, should I tell them just not to accept the deliveries?  I've been a loyal Dell customer for years, but those days are over. So disappointed. 
Cancelled Order but Shipped Anyway