I haven't received a notice of enlistment for one year.

Legal analysis: it should belong to the armed forces department where the school is located. The notice of enlistment was sent there. The armed forces department you came to has no information about your son's enlistment, so it's normal not to receive it. If you lose your notice of enlistment, you can go to the armed forces department where you signed up to join the army and ask them to check your son's information and issue a certificate stamped with the official seal, which is as useful as the notice of enlistment.

Legal basis: Article 26 of the Regulations on Conscription, county and city conscription offices shall go through the formalities of enlistment, issue a notice of conscription to citizens, and notify the household registration authority where their permanent residence is located. Family members shall cancel the registered residence of citizens applying for enlistment at the household registration authority where the permanent residence is located by the notice of enlistment, and enjoy the treatment of family members of the army.