is DSS/private or gov't/subsidy school ? It would not be happened if it belongs to the ladder type.
If DSS/private -- nothing to do on it as they have prioritized their students.
If gov't/subsidy --- you can check with the ED board directly and also look for the main reasons on causing this mistake from the school. Overlook is not a point as they do the same on each year. Have the school mentioned
due to inadequate space or what?
Don't mess up the whole thing yourself. I think the reply from the principal already assure you that a place has been reserved for you. Unless.....you are acting like a trouble-maker now !!