Can you create a new New Quiz and build that one, or do you get the same error?
Given that it's a paid account, you technically should have access to New Quizzes, but they can be enabled/disabled by an Admin, so @NoahBoswell's point could still be applicable - trying to create a New Quiz would rule that out.
I tried disabling New Quizzes in my own course setting (I'm a mere faculty, so can't test Admin settings), and while it disabled the creation of a new New Quiz, it still allowed me to build an existing New Quiz, so that's the opposite of your issue. But Admin settings probably works differently.