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You can appeal, but it will not change the outcome - unless you change your circumstances in a way that makes you eligible for an extension (which, right now, you are obviously not).
Why do you want to stay in Singapore that long?Is that a justified reason (as defined by ICA)?

I have a son and baby 2yo who stay here in sg. Im waiting for the vaccine for my son, But i didnt got an email. Only in ica website that said "you required to leave in singapore" can still appeal?

You can visit direct to any polyclinic.
Or May be call them and book an appointment.

Only Long term visa allowed at this moment to make an appointment for vaccine.

Your story is still too confusing to make sense out of it.
If you have two kids living in Singapore, you can apply for a DP or LTVP.
But if you can't get any other visa (and no extension), you must leave Singapore by 28.Aug.

You can try to walk-in at ICA, approach the VCS desk and explain your wish to get extension. They will ask you to fill up the visa application form and give you a Queue number to speak to an officer. I did this today out of pure determination as my daughter's STVP is expiring on the 21st. We successfully got  her STVP extended after getting rejected 3x in the last 8 days. The officer mentioned to me, for online request, they pretty much still base on the dates as per Disembarkation Card and it was good that we came.

But remember, you should have a considerable reason why you want to extend. In our case, my daughter is waiting for full vaccination to take effect and has an existing STP appeal.