£90 charge for unreturned kit

In March this year, I received a replacement Virgin TV 360 box and returned the old one via Yodel using the label provided.

Today I have had yet another text message and email reminding me that a £90 charge has been applied to my account for unreturned kit. I have been getting similar messages since the 3 May, and have contacted Virgin Media twice to advise that I had in fact returned the kit (on 16 March): both times I was told not to worry as it can take up to 10 days for the kit to arrive at their depot. I told them it was well over 10 days ago and was assured that I would not be charged. But today, another reminder...

I have provided the Yodel reference number for the return, but without the postcode I personally cannot check to see that the box arrived safely. When I mentioned this in one of my calls, I was told they couldn't give me the postcode as Virgin has lots of depots across the country.

Has anyone else had a similar experience? How long did it go on for? Were you actually charged?

Thanks in advance!