Does game pass ultimate cancel my 12 month gold subscription?

If you add a prepaid gold or game pass while you have an active Ultimate subscription, it will be converted to Ultimate since Ultimate includes gold and game pass (it does warn you before you complete the transaction). The codes are converted based on
price rather than time. 12 months of Gold is equal to the price of 4 months of Ultimate. In order to use just the full 12 months of Gold, you have to add the code after your Ultimate subscription ends or you cancel it and it has ended.

When you added the card were you on an Ultimate Game Pass subscription? Adding gold while on Ultimate will convert the gold to Ultimate. A 12 month subscription is converted to 4 months of Ultimate.

Otherwise, you may want to verify the subscription at http://account.microsoft.com to see if it does show any errors or if the subscription was cancelled. If it does and it was indeed
a 12 month that was added, you'll want to contact support. http://support.xbox.com/contact-us

If you add a 12 month Gold or standard Game Pass code while you have an active Game Pass Ultimate subscription, it will be converted to Ultimate. 12 months of Gold is equal to 4 months of Ultimate. In order to keep the full 12 months, you have to cancel your Ultimate or let it run out before you add the new code.

Technically you're not. Gold and Game Pass are converted into Ultimate based on price, not based on the time. The price for 4 months of Ultimate is the same price as 12 months of gold. If you want to use the full 12 months of just Gold, you would need
to cancel Ultimate or wait for your Ultimate subscription to expire and then add the 12 months.

Since Game Pass Ultimate includes Gold, when you add a Gold card to an Ultimate subscription, it converts the Gold to Ultimate as well. Since 12 months of Gold is equal in price to 4 months of Ultimate, that is what it converts it to. In order to use a full 12 month Gold card, you have to either cancel your Ultimate subscription or let it fully expire before adding the new card.