Converting gold to ultimate

So right now, i have a prepaid 12 month subscription for xbox live gold. If i want to upgrade it to ultimate, first it shows me that it costs only 1 euro, but when i click on it, it shows me the original price. Why? And the other question is that if i upgrade it to ultimate, will i get 12 month of ultimate or just 3 month? I'm a little bit confused.

Thanks for the answers in advance.

:)