Cannot purchase ANY Xbox 360 backward compatible game on Xbox One

Have had this problem since Saturday, I've reached out on multiple platforms to Xbox/Microsoft Support with no success.

Every time I attempt to purchase an Xbox 360 backward compatible game, I get the following error: "Sorry. Your purchase cannot be completed at this time. Please try again."

Let's go down the list of things it is NOT, before I get a bot responding to me with unhelpful guesses as to what it is:

It is NOT a credit card issue. I have tried a different card, same error. Both cards are valid.

It is NOT a console issue. I get the same error if I try to purchase a game on marketplace.xbox.com.

It is NOT a region lock issue. The game(s) I am attempting to purchase are purchasable in my region.

It is NOT a Child Account issue. I am not purchasing from a Child account. I do not have a Child account.

It is NOT specific to one Xbox 360 title. No matter what title I attempt to purchase, be it a game or DLC, I get the same error.

I contacted Xbox Support, and got the following unhelpful responses from MIcrosoft Answer Techs:

"Remove all your credit card information from your Microsoft account, wait 24 hours, re-add it, and try again."

I did. Same error.

"Backward Compatible Xbox 360 games are not purchasable through or for Xbox One."

This is just completely false. Backward Compatibility not only exists on Xbox One, it is a FEATURE of Xbox One.

I then contacted @XboxSupport on Twitter, and immediately received a nonsensical reply from a bot claiming to rep Xbox Support.

"We're experiencing heavy volume at the moment. Wait times for refund requests, contacting us, and other support services may be longer than usual."

First of all, I didn't ask about wait times. I asked if someone, ANYONE at @XBoxSupport could help me (SUPPORT me!) with my issue, and the response I get is the Twitter equivalent of, "Please stay on the line."

Power cycling does nothing. As I said above, it is NOT a console issue.

I am able to purchase games/movies/etc. from Microsoft/Xbox One. This affects ONLY the Xbox 360 Marketplace.

I do not, have not, will never own an Xbox 360, so purchasing directly from there is not/will never be an option.

I have been told by support that this is an issue that is affecting multiple users, all with correct payment information. However, I see NO discussion of this anywhere on the Internet. If MANY PEOPLE are suddenly unable to use a PROMOTED FEATURE (backward
compatibility) on their console, why aren't people discussing it, then?

Which leads me to believe that the issue is isolated to my account, and there is nothing I can do since it is very obviously a problem on Microsoft's end that only THEY can undo.

So... am I just frozen out of buying Xbox 360 games forever for absolutely no reason, or can someone over there actually resolve this issue without giving me a off-topic, scripted reply?

:)