Returned kit apperently not received?

Hi. I had an "Upgrade" to Hub 4 from Hub 3 recently and returned the old Hub 3 as instructed. This was sent back using my local Yodel collection point and I have an email confirming this. When I track the packege it shows it has been delivered back to Virgin. Why then do they still keep harrassing me with reminders to return the Kit?, this is happenning every week now and trying to contact them by phone is useless. As usual Virgin customer service is the wosrt on the planet!