Mine has done the same thing. I have all prerequesites filled to get the quest and shalidor and valaste are nowhere to be found. I have tried a myriad of "fixes" support chat suggested but not one of them worked. Kind of a pain because they take about a week to send each email and the fix does nothing. Waiting on their fourth email now... Really wish they would fix this as the reward for the final quest can be quite beneficial...
I am having the same issue. I've reached all the prerequisite lvls in Mage guild level which is 5 and am already at VR2 on my character. Been to most all of mages guild halls. No Shalidor or Valaste anywhere.