Can I refuse delivery of something?

the_lunatic_is_in_my_head

As above from Shaun the customer must pay the return postage if the terms are correct, have been provided before the point of sale (along with the other required information) and after the sale via durable means (typically email or a hard copy included with the goods on paper) and that the terms state the customer is responsible for the return costs. The customer can cancel at any point including before receipt.

Argos CS might not help you out because they have a script to stick to but phoning Head Office and asking for the team at the MD's office would see a refund, however I'm pretty sure Argos would refund upon receipt of the refused item regardless of asking to cancel.

You do still need to cancel via email just incase as without the request to cancel the right to cancel doesn't need to be adhered to and a deduction from the original payment could be permissible (if stated in the terms).