Cannot cancel game pass

It just means that you cannot cancel the 24 months of game pass ultimate to reduce the payments. The console is still yours after the payments.

You would be best placed to create your own thread.

If you are referring to losing Xbox Live Gold because you cancelled Game Pass Ultimate, there is nothing that can be done. It clearly states that Xbox Live Gold will be converted to Game Pass Ultimate days and can not be reverted and that canceling Game
Pass Ultimate will cancel out the converted Xbox Live Gold. https://support.xbox.com/en-US/billing/xbox-subscriptions/xbox-game-pass-ultimate-faq

You can cancel your Game Pass Ultimate membership at any time, and you will
continue to have access to your Ultimate benefits until your prepaid time ends, at which point you will not be charged again.

Note The upgrade of any prepaid time to Xbox Game Pass Ultimate cannot be reverted back to Xbox Live Gold or Xbox Game Pass, and you cannot receive a refund for Xbox Live Gold or Xbox Game
Pass. You can, however, rejoin Xbox Live Gold or Xbox Game Pass when your Xbox Game Pass Ultimate subscription ends

It didn't work, and neither did removing Gaming Services with Powershell, then reinstalling.

It's starting to seem like this cannot be fixed. In which case I may as well cancel Game Pass :/

When you purchased the promotional price, anything you had on your account was converted to Ultimate Game Pass (that is stated in the promotion) and cannot be converted back. So by confirming your purchase for the promotion, you agreed to that. Cancelling
the subscription would cancel your Ultimate Game Pass which included the now converted gold. You would have to purchase a new subscription.

You would have to buy a new Gold subscription. The Gold would have been cancelled when it was converted to Game Pass Ultimate and cannot be reverted once that happens.