Yeah you will have to try. This is the first we have a Singapore PR who lives and studies in Malaysia who gets caught up in this because of SPM age vs O-level age.
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Side discussion for additional thought: If my assumptions below are true, what do you think your parents would feel right now, knowing that their strategy to avoid you from doing NS, a decision they made when you are young and incapable by...?:
1. Keeping your SG PR but keeping you in Malaysia
2. Keeping your sisters (SG PRs) in Singapore
3. Putting you through very inferior Malaysia education system, undermining your real potential in tertiary education, employment and immigration opportunities globally
4. While your sisters are in advantageous Singapore education system (not perfect but still better), giving them not only one-year headstart due to NS obligation on their male peers, but also an (probably) exponential opportunities compared to you specifically
5. Exposing you to a risk of burning bridges with Singapore for life (employment, education, family/friend interaction, even flight transit in Singapore) should you/your family choose to run away from NS and be listed as NS defaulter and put on immigration watch list. - honestly I think this part has very low risk because from your posting, you exhibited sincerity to obey the NS law despite of potential disruption to your current education level
I hope you're not taking these words wrongly. I am typing this with a hand over my heart (figuratively, I still need two hands to type) but I really feel a lot for poor children like you (and many others who sought help here), who are subjected to potentially permanent damage to their path in life because of their parents' poor thought and opportunistic intention. Even if this is true, I am sure your parents had parental loving intention for you when they decided to pull this stunt but if they really meant well for your future, they should have done their homework to avoid this problem in decades to come, or even better, to NEVER ever consider abetting you into skipping NS in the first thought.