Thanks for the useful post. For the sake of experimenting, I made my request for a partial refund on Prime by just being polite and saying I had no use for the additional services and just wanted Prime. I was told that no, I couldn't get a partial refund, but he could cancel my Prime subscription altogether - He would've said this knowing very well that I wouldn't cancel, as I use Prime almost daily.
I then gave him a link to your post and after a few minutes of delay, he responded:
"Normally, we do not issue a partial refund for the prime membership, because prime is an all you can eat package.
The link that you provided was given to a customer as a one time exception as the customer was very frustrated about the charge of the prime membership.
However, I'll make an one time exception to our policy and issue a partial refund for your prime membership."
So thanks for the post and setting the precedent to make the discussion easier for the rest of us 🙂