Xbox Live Gold code says redeemed; no indication code worked

This is long-winded, but please bear with me.

Earlier this month, I "purchased" a three-month subscription for XBL Gold using Microsoft Rewards points. The code came via e-mail,

just as they always have the various times I had also redeemed points for an extension of my Gold subscription.

As it turns out, I was a day late in ordering the three months with Rewards points, so my PayPal was charged for a single month of Gold service. Cool. So at this point, my Gold service extends to December. A three-month subscription through Rewards point
redemption would push that to March 2020, right?

I copied the code from the e-mail to the Xbox Redeem Code page in Edge. I was then told the code had already been redeemed. How is that possible, seeing as how the first time I ever saw the code was when I copied it from e-mail?

Thinking this was perhaps a Microsoft Rewards issue, as the transaction was described as "Pending" for several days after my purchase, I contacted Rewards support for help. I was referred to Xbox support and that particular case/ticket/what-have-you was
closed. No problem there, though it doesn't explain why my order was listed as "Pending" when I certainly received a code. Why would a transaction be shown to be in an in-process state when the customer received what they had ordered?

Yesterday, I contacted Xbox support for help. After clearly explaining that while I had input the code only to find it had been redeemed ***before my first attempt to redeem it***, the tech handling my case said, "The code has already been redeemed against
your account." How? Why? If the code had been redeemed successfully, wouldn't my Gold subscription reflect that three-month extension? And along with the tech's short-but-not-so-sweet "explanation", I also got a separate e-mail saying that this case was closed.

Once again, I contacted Xbox support--the same tech, the same case number, all that, but this time I attached screenshots showing that while everything *says* the code was redeemed, my Gold service does *not* show that the code worked. Like I never received
a code at all.

The tech's response was the same as when he closed the case. The exact same wording, cut-and-paste. And I received another e-mail saying the case had been closed.

What. The. What.

So as it stands right now, I am out 20,000 Rewards points (not a small amount) and nothing to show for it but a headache and a sour experience with MS tech support. Any help from this forum would be greatly appreciated, as I don't know what else to do to
help get this situation to a satisfactory conclusion.

:)