Hi @Bradst
I suspect this is because the subscription is still valid on your previous contract, the subscription will be valid until the end of contract or when the contract is cancelled.
When you mention you have taken out a new SIM only contact, this will be an upgrade with a new Prime subscription and the previous subscription will need to be cancelled, when it has run it's course until the next monthly renewal date, you will be able to opt into the new subscription that comes with your upgrade. There is a previous thread here: https://forum.vodafone.co.uk/t5/Pay-monthly/Vodafone-Amazon-Prime-Video-subscription-will-not-cancel... but the link to cancel is no longer valid on the website and the best alternative I can find is here: Cancel Entertainment
I would recommend letting the Social Team sort this out for you, they will have the necessary account account and get the Prime onto the new contract. They will be contacted through Twitter/Facebook here: Contact Us
