Unable to purchase Xbox games (even free ones)

I was trying to purchase an Xbox 360 game for Xbox One S (Backwards compatible), but when I try to purchase the game, I get an error about buying the game from the Xbox itself and not xbox.com even though I tried to complete the purchase from the Xbox, or
(when trying to complete the purchase from marketplace.xbox.com at a computer) I get sent to the xbox.com home page when clicking on "Buy Game." I have tried using a different account, and that account was able to get to the purchase screen. I did notice that
xbox.com does not show me as logged in (logging in with the other account worked fine, other Microsoft websites show me as logged in). The "Sign In" button was there, but there was no blank user icon and the "Sign In" text was no longer a button (again, worked
fine with a different account). I know that my account is capable of purchasing content, I have purchased Cuphead and several other free games, but now I cannot even purchase a free title. I have checked for cookie issues, none seem present; I have tried different
browsers, no difference; and I have restarted the Xbox itself, it didn't fix any issues. xbox.com/status shows everything as operational. I also cannot sign onto account.xbox.com to view my profile.

EDIT: The websites are also very inconsistent on whether or not they show my gamertag and image, answers.microsoft.com shows my gamertag and image, but non of the other domains (that I have noticed) show it, they only show my name and my profile icon. And
the "My Profile" link only shows up for answers.microsoft.com and links to that profile. I cannot get to my Xbox profile anywhere. I can go to account.xbox.com, but it just sends me to this
support page. I am not a part of a Microsoft family, my account is a single, lone account.

TL;DR: I cannot purchase anything on my Xbox account (via Xbox or web). Xbox.com does not show me as signed in (other MS domains show me as signed in)

:)