Returning Virgin kit back

Hi
I have closed my Virgin Media account, and, two week ago exactly, I sent the kit back following the instructions from Virgin Media.
I have just received and email stating that I would charged 130.00 on 07-Jan if the kit is not received. I actually have no way to prove that I sent the kit back. Yodel, after they scanned the box in, told me that they didn't give receipts. 
Could some from VM team help confirming my return? If the shipment got lost, how do I avoid getting charged for something that is not my fault.

Artur