I would call again and request for the teacher you did want. Perhaps the school may want to know the reason as that may make them more lenient to switch your son to the teacher you want.

Alternatively, if you still cannot get the change, you can have your son grin and bare it. Consider a teacher to be a boss or an employer, and throughout life, we're going to get bosses or employers who we're not too fond of but continue anyways.