You can print your own label. Go to this page https://www.collectplus.co.uk/virgin
Scroll down and click on create new label. Where it says customer reference number either enter Virgin Media account number, or the serial number of the equipment being returned.
Then enter your email address, and click on email me my new label and follow the instructions
You can find your local Collect Plus point here store-locator
The shopkeeper will scan your parcel and give you a receipt with a unique reference code - keep this handy as proof - and don't forget to include a covering letter with your equipment with your name and account number.
The return kits are scanned into VM systems in bulk so it may take a while for your account to be updated to indicate the equipment has been returned, and in the meantime you will probably still receive emails asking to return the kit
Dave
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali