Here's my story - posting from DD article comments, hadn't seen this thread until now that Dan posted it.
I had ordered 13 of these. I’ve been receiving them 1-2 at a time for the past 2 months, and I just now finished receiving them all. First 7 I was charged the correct $21 plus tax, the last 6 I was charged $47.99 plus tax and the invoices now reflect that in my Amazon account (the invoice shows the $46.99 prime savings but removes the additional $26.99 prime savings). After lengthy call with Amazon, they said they do see there was an error with the promotions on the orders that billed the higher amount. They said they will refund the difference, but cannot do it from their end, so sending over all the information to the marketing and promotions department, and they should take care of it and email me within a day. I will try to post follow up here once updated.
Follow up –
Marketing and promotions department emailed me within an hour, but they did not have the whole story like they were supposed to, and I had to explain it to them all again. It was a little hard replying to their emails, because it didn’t usually let replies. After sending email with screenshots of confirmation emails, they refunded the $26.99 mischarge amount per tablet, but not the tax I was charged. Took more phone calls and a live chat until they told me they have to send it to the tax department, and a couple days later they refunded me the tax (actually they over-refunded me a total of $8 and change, but I think I deserve it). Also got a $5 promo for next order thrown in from the live chat.
I’m shocked Amazon can do such a thing without any apologies, etc. It has to be against their terms.