BT offering single billing for Amazon Prime Video.
New and existing BT TV customers who recontract can sign up for Amazon Prime Video and enjoy six months of award-winning TV shows, films, and sport at no extra cost courtesy of BT via the Prime Video app on BT TV, providing they don't want to use an existing Amazon Prime Video account. The new Prime Video account will then be billed as part of the customer's main BT bill.
The first customers to take up the offer will receive their six months subscription in time for Prime Video’s first Premier League games this December. Prime Video will show two full Premier League rounds consisting of 20 matches, for the very first time this season.
Additionally, BT TV customers will also benefit from the added convenience of using their Amazon Alexa-enabled device (including Amazon Echo and Echo Dot) to search for all their favourite movies, TV and sport for the first time. Customers can link BT TV to their Alexa account by enabling the BT TV skill via the Alexa app.
Not for those of us on the top package (4K package) https://tv.bt.com/tv/amazon-prime-video-on-bt-tv/how-to-get-amazon-prime-video-bt-tv-11364301945669
If you're a new BT TV customer or if you’re upgrading your TV package, we’re giving you an extra special treat – six months of Prime Video on us.
If you already have BT TV and you’re happy with your current package, you can add Prime Video and get 30 days on us.
This question was also asked here https://community.bt.com/t5/Bills-Packages/free-6-months-amazon-prime-video/m-p/1985392#M114486
So If you look at the reply from a moderator, on that thread, you should get the answer.