John
They usually overbook the appointments and therefore unable to deal with staff absences.
You did not have to accept the appointment for the next day as you are entitled to seven days written notice but having accepted it you are now committed to attending.
If you have not changed the appointment yourself, then you are still entitled to do this once, so can rearrange for a date more convenient for your son to attend with you.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
