Virgin... the gift that keeps on giving, not!

Hi

I ended my contract with Virgin recently (the inability to speak to an actual person tipped me over the edge) and returned, as requested, all three items. I clearly followed the instructions that involved wrapping one of the items in a separate bag inside the main bag. 

I got an email today to say that the router and pod have been received but the tv streaming box hasn't. I know I returned it (we never used it and it was sat in a box by the side of the TV where it had been since day one) but how can I prove it? Of course Virgin will want to charge me £45 for not returning something I have returned. 

I am kicking myself for not taking a photo as evidence but I was so keen to cut ties with Virgin, I rushed to get it back. Does anyone have an suggestions?

The answers from the Virgin team on here have been the only way I've had any joy during my contract with them so hoping someone can help! 

Thanks.