At that point in both the Doctor and Clara's personal history, not only did 12 not exist but _he never would_, because the Doctor was fated to die permanently in Christmas, on Trenzalore. It was only a later timeline change that introduced 12 and onwards to the Universe.

Unfortunately, the cameo appearance of Capaldi in _The Day of the Doctor_ totally ruins that but there we go; blame dramatic licence for that one, I guess.