how long has ur permit lapsed? have you ever applied for any deferments or permits since your ord?
have you logged in to ns.sg and seen if you have any notices?
were you assigned a unit before you left? have you/your family received any call-up letters since you left?
each year is about 1k iirc. if you can’t pay you up you’ll likely go to prison. probably won’t be long. like maybe a week for a 5k fine?
good luck!