Why did I only get 4 months using a code for 12 months?

if you already had ultimate or you took the offer for ultimate it converts 12 gold into 4 months of ultimate. if you did not want this contact support directly.

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.

if you already had ultimate or you took the offer for ultimate it converts 12 gold into 4 months of ultimate. if you did not want this contact support directly.

I am scouring this site to find out how to contact them directly. Where do I do that?

Go to http://beta.support.xbox.com/contact-us If you don't see the options to request a call back or chat with support, change your category/topic until you do. Billing
& Subscriptions and "I don't recognize a charge" usually works.

Did you have Game Pass Ultimate at the time you added the code and may have added a 12 month Gold or standard Game Pass (not Ultimate) code? That would cause the code to be added for 4 months rather than 12.