I sympathise because something similar happened to me, except the item also appeared on my credit card. I think the scam was either someone was planning on intercepting it, or that the person who had ordered it had done so through a cashback website such as quidco and was earning a large cashback.
�1300 line rental? How long a period does that cover?
I know it's too late now, but with hindsight it's a good idea to agree on postage arrangements when they ask you to return something. You could even have asked them to collect.